8215281: Use String.isEmpty() when applicable in java.base

Reviewed-by: dfuchs, alanb

src/java.base/share/classes/com/sun/java/util/jar/pack/Attribute.java

@@ -996,7 +996,7 @@ class Attribute implements Comparable<Attribute> {
                             endp = cstr.indexOf(',', cp);
                             if (endp < 0)  endp = cstrlen;
                             String cstr1 = cstr.substring(cp, endp);
-                            if (cstr1.length() == 0)
+                            if (cstr1.isEmpty())
                                 cstr1 = "empty";  // will fail parse
                             int value0, value1;
                             // Check for a case range (new in 1.6).

src/java.base/share/classes/com/sun/java/util/jar/pack/Driver.java

@@ -279,7 +279,7 @@ class Driver {
         junpack.properties().putAll(engProps);
         if (doRepack && newfile.equals(jarfile)) {
             String zipc = getZipComment(jarfile);
-            if (verbose && zipc.length() > 0)
+            if (verbose && !zipc.isEmpty())
                 System.out.println(MessageFormat.format(RESOURCE.getString(DriverResource.DETECTED_ZIP_COMMENT), zipc));
             if (zipc.indexOf(Utils.PACK_ZIP_ARCHIVE_MARKER_COMMENT) >= 0) {
                     System.out.println(MessageFormat.format(RESOURCE.getString(DriverResource.SKIP_FOR_REPACKED), jarfile));
@@ -552,7 +552,7 @@ class Driver {
             if (words.length == 0)    continue loadOptmap;
             String opt = words[0];
             words[0] = "";  // initial word is not a spec
-            if (opt.length() == 0 && words.length >= 1) {
+            if (opt.isEmpty() && words.length >= 1) {
                 opt = words[1];  // initial "word" is empty due to leading ' '
                 words[1] = "";
             }
@@ -622,7 +622,7 @@ class Driver {
                     switch (specop) {
                     case '+':
                         // + means we want an non-empty val suffix.
-                        ok = (val.length() != 0);
+                        ok = !val.isEmpty();
                         specop = spec.charAt(sidx++);
                         break;
                     case '*':
@@ -641,10 +641,10 @@ class Driver {
                     String specarg = spec.substring(sidx);
                     switch (specop) {
                     case '.':  // terminate the option sequence
-                        resultString = (specarg.length() != 0)? specarg.intern(): opt;
+                        resultString = specarg.isEmpty() ? opt : specarg.intern();
                         break doArgs;
                     case '?':  // abort the option sequence
-                        resultString = (specarg.length() != 0)? specarg.intern(): arg;
+                        resultString = specarg.isEmpty() ? arg : specarg.intern();
                         isError = true;
                         break eachSpec;
                     case '@':  // change the effective opt name
@@ -655,14 +655,14 @@ class Driver {
                         val = "";
                         break;
                     case '!':  // negation option
-                        String negopt = (specarg.length() != 0)? specarg.intern(): opt;
+                        String negopt = specarg.isEmpty() ? opt : specarg.intern();
                         properties.remove(negopt);
                         properties.put(negopt, null);  // leave placeholder
                         didAction = true;
                         break;
                     case '$':  // normal "boolean" option
                         String boolval;
-                        if (specarg.length() != 0) {
+                        if (!specarg.isEmpty()) {
                             // If there is a given spec token, store it.
                             boolval = specarg;
                         } else {

src/java.base/share/classes/com/sun/net/ssl/KeyManagerFactory.java

@@ -153,7 +153,7 @@ public class KeyManagerFactory {
                                                  String provider)
         throws NoSuchAlgorithmException, NoSuchProviderException
     {
-        if (provider == null || provider.length() == 0)
+        if (provider == null || provider.isEmpty())
             throw new IllegalArgumentException("missing provider");
         Object[] objs = SSLSecurity.getImpl(algorithm, "KeyManagerFactory",
                                             provider);

src/java.base/share/classes/com/sun/net/ssl/SSLContext.java

@@ -109,7 +109,7 @@ public class SSLContext {
     public static SSLContext getInstance(String protocol, String provider)
         throws NoSuchAlgorithmException, NoSuchProviderException
     {
-        if (provider == null || provider.length() == 0)
+        if (provider == null || provider.isEmpty())
             throw new IllegalArgumentException("missing provider");
         Object[] objs = SSLSecurity.getImpl(protocol, "SSLContext",
                                             provider);

src/java.base/share/classes/com/sun/net/ssl/TrustManagerFactory.java

@@ -155,7 +155,7 @@ public class TrustManagerFactory {
                                                  String provider)
         throws NoSuchAlgorithmException, NoSuchProviderException
     {
-        if (provider == null || provider.length() == 0)
+        if (provider == null || provider.isEmpty())
             throw new IllegalArgumentException("missing provider");
         Object[] objs = SSLSecurity.getImpl(algorithm, "TrustManagerFactory",
                                             provider);

src/java.base/share/classes/java/io/Console.java

@@ -247,7 +247,7 @@ public final class Console implements Flushable
         String line = null;
         synchronized (writeLock) {
             synchronized(readLock) {
-                if (fmt.length() != 0)
+                if (!fmt.isEmpty())
                     pw.format(fmt, args);
                 try {
                     char[] ca = readline(false);
@@ -319,7 +319,7 @@ public final class Console implements Flushable
                 }
                 IOError ioe = null;
                 try {
-                    if (fmt.length() != 0)
+                    if (!fmt.isEmpty())
                         pw.format(fmt, args);
                     passwd = readline(true);
                 } catch (IOException x) {

src/java.base/share/classes/java/lang/ClassLoader.java

@@ -1119,7 +1119,7 @@ public abstract class ClassLoader {
 
     // true if the name is null or has the potential to be a valid binary name
     private boolean checkName(String name) {
-        if ((name == null) || (name.length() == 0))
+        if ((name == null) || (name.isEmpty()))
             return true;
         if ((name.indexOf('/') != -1) || (name.charAt(0) == '['))
             return false;

src/java.base/share/classes/java/lang/Integer.java

@@ -1409,7 +1409,7 @@ public final class Integer extends Number
         boolean negative = false;
         Integer result;
 
-        if (nm.length() == 0)
+        if (nm.isEmpty())
             throw new NumberFormatException("Zero length string");
         char firstChar = nm.charAt(0);
         // Handle sign, if present

src/java.base/share/classes/java/lang/Long.java

@@ -1248,7 +1248,7 @@ public final class Long extends Number
         boolean negative = false;
         Long result;
 
-        if (nm.length() == 0)
+        if (nm.isEmpty())
             throw new NumberFormatException("Zero length string");
         char firstChar = nm.charAt(0);
         // Handle sign, if present

src/java.base/share/classes/java/lang/Package.java

@@ -397,11 +397,11 @@ public class Package extends NamedPackage implements java.lang.reflect.Annotated
     public String toString() {
         String spec = versionInfo.specTitle;
         String ver =  versionInfo.specVersion;
-        if (spec != null && spec.length() > 0)
+        if (spec != null && !spec.isEmpty())
             spec = ", " + spec;
         else
             spec = "";
-        if (ver != null && ver.length() > 0)
+        if (ver != null && !ver.isEmpty())
             ver = ", version " + ver;
         else
             ver = "";

src/java.base/share/classes/java/lang/Runtime.java

@@ -403,7 +403,7 @@ public class Runtime {
      */
     public Process exec(String command, String[] envp, File dir)
         throws IOException {
-        if (command.length() == 0)
+        if (command.isEmpty())
             throw new IllegalArgumentException("Empty command");
 
         StringTokenizer st = new StringTokenizer(command);

src/java.base/share/classes/java/lang/String.java

@@ -664,7 +664,7 @@ public final class String
      *          object.
      */
     public int length() {
-        return value.length >> coder();
+        return isLatin1() ? value.length : value.length >> UTF16;
     }
 
     /**
@@ -1943,8 +1943,7 @@ public final class String
      *          characters followed by the string argument's characters.
      */
     public String concat(String str) {
-        int olen = str.length();
+        if (str.isEmpty()) {
-        if (olen == 0) {
             return this;
         }
         if (coder() == str.coder()) {
@@ -1956,6 +1955,7 @@ public final class String
             return new String(buf, coder);
         }
         int len = length();
+        int olen = str.length();
         byte[] buf = StringUTF16.newBytesFor(len + olen);
         getBytes(buf, 0, UTF16);
         str.getBytes(buf, len, UTF16);
@@ -2316,7 +2316,7 @@ public final class String
             // Construct result
             int resultSize = list.size();
             if (limit == 0) {
-                while (resultSize > 0 && list.get(resultSize - 1).length() == 0) {
+                while (resultSize > 0 && list.get(resultSize - 1).isEmpty()) {
                     resultSize--;
                 }
             }

src/java.base/share/classes/java/lang/VersionProps.java.template

@@ -73,7 +73,7 @@ class VersionProps {
         "@@VENDOR_VERSION_STRING@@";
 
     private static final String vendor_version =
-        (VENDOR_VERSION_STRING.length() > 0
+        (!VENDOR_VERSION_STRING.isEmpty()
          ? " " + VENDOR_VERSION_STRING : "");
 
     private static final String VENDOR =
@@ -95,7 +95,7 @@ class VersionProps {
         props.put("java.version.date", java_version_date);
         props.put("java.runtime.version", java_runtime_version);
         props.put("java.runtime.name", java_runtime_name);
-        if (VENDOR_VERSION_STRING.length() > 0)
+        if (!VENDOR_VERSION_STRING.isEmpty())
             props.put("java.vendor.version", VENDOR_VERSION_STRING);
 
         props.put("java.class.version", CLASSFILE_MAJOR_MINOR);

src/java.base/share/classes/java/lang/invoke/ConstantBootstraps.java

@@ -103,7 +103,7 @@ public final class ConstantBootstraps {
         if (type != Class.class) {
             throw new IllegalArgumentException();
         }
-        if (name.length() == 0 || name.length() > 1) {
+        if (name.length() != 1) {
             throw new IllegalArgumentException(String.format("not primitive: %s", name));
         }
 

src/java.base/share/classes/java/lang/invoke/MethodHandles.java

@@ -201,7 +201,7 @@ public class MethodHandles {
             throw new IllegalAccessException(callerModule + " does not read " + targetModule);
         if (targetModule.isNamed()) {
             String pn = targetClass.getPackageName();
-            assert pn.length() > 0 : "unnamed package cannot be in named module";
+            assert !pn.isEmpty() : "unnamed package cannot be in named module";
             if (!targetModule.isOpen(pn, callerModule))
                 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
         }

src/java.base/share/classes/java/lang/invoke/ProxyClassesDumper.java

@@ -62,7 +62,7 @@ final class ProxyClassesDumper {
         }
         try {
             path = path.trim();
-            final Path dir = Path.of(path.length() == 0 ? "." : path);
+            final Path dir = Path.of(path.isEmpty() ? "." : path);
             AccessController.doPrivileged(new PrivilegedAction<>() {
                     @Override
                     public Void run() {

src/java.base/share/classes/java/net/HttpCookie.java

@@ -149,7 +149,7 @@ public final class HttpCookie implements Cloneable {
      */
     HttpCookie(String name, String value, String header, long creationTime) {
         name = name.trim();
-        if (name.length() == 0 || !isToken(name) || name.charAt(0) == '$') {
+        if (name.isEmpty() || !isToken(name) || name.charAt(0) == '$') {
             throw new IllegalArgumentException("Illegal cookie name");
         }
 

src/java.base/share/classes/java/net/Inet6Address.java

@@ -433,7 +433,7 @@ class Inet6Address extends InetAddress {
                                             NetworkInterface nif)
         throws UnknownHostException
     {
-        if (host != null && host.length() > 0 && host.charAt(0) == '[') {
+        if (host != null && !host.isEmpty() && host.charAt(0) == '[') {
             if (host.charAt(host.length()-1) == ']') {
                 host = host.substring(1, host.length() -1);
             }
@@ -466,7 +466,7 @@ class Inet6Address extends InetAddress {
                                             int scope_id)
         throws UnknownHostException
     {
-        if (host != null && host.length() > 0 && host.charAt(0) == '[') {
+        if (host != null && !host.isEmpty() && host.charAt(0) == '[') {
             if (host.charAt(host.length()-1) == ']') {
                 host = host.substring(1, host.length() -1);
             }
@@ -601,7 +601,7 @@ class Inet6Address extends InetAddress {
         boolean scope_ifname_set = gf.get("scope_ifname_set", false);
         String ifname = (String)gf.get("ifname", null);
 
-        if (ifname != null && !"".equals (ifname)) {
+        if (ifname != null && !ifname.isEmpty()) {
             try {
                 scope_ifname = NetworkInterface.getByName(ifname);
                 if (scope_ifname == null) {

src/java.base/share/classes/java/net/InetAddress.java

@@ -1187,7 +1187,7 @@ class InetAddress implements java.io.Serializable {
      */
     public static InetAddress getByAddress(String host, byte[] addr)
         throws UnknownHostException {
-        if (host != null && host.length() > 0 && host.charAt(0) == '[') {
+        if (host != null && !host.isEmpty() && host.charAt(0) == '[') {
             if (host.charAt(host.length()-1) == ']') {
                 host = host.substring(1, host.length() -1);
             }
@@ -1301,7 +1301,7 @@ class InetAddress implements java.io.Serializable {
     private static InetAddress[] getAllByName(String host, InetAddress reqAddr)
         throws UnknownHostException {
 
-        if (host == null || host.length() == 0) {
+        if (host == null || host.isEmpty()) {
             InetAddress[] ret = new InetAddress[1];
             ret[0] = impl.loopbackAddress();
             return ret;

src/java.base/share/classes/java/net/SocketPermission.java

@@ -460,7 +460,7 @@ public final class SocketPermission extends Permission
             }
             return;
         } else {
-            if (host.length() > 0) {
+            if (!host.isEmpty()) {
                 // see if we are being initialized with an IP address.
                 char ch = host.charAt(0);
                 if (ch == ':' || Character.digit(ch, 16) != -1) {
@@ -705,8 +705,7 @@ public final class SocketPermission extends Permission
                                       .orElse(b);
         }
 
-        return cdomain.length() != 0 && hdomain.length() != 0
+        return !cdomain.isEmpty() && !hdomain.isEmpty() && cdomain.equals(hdomain);
-                        && cdomain.equals(hdomain);
     }
 
     private boolean authorized(String cname, byte[] addr) {

src/java.base/share/classes/java/net/URI.java

@@ -1959,10 +1959,8 @@ public final class URI
         throws URISyntaxException
     {
         if (scheme != null) {
-            if ((path != null)
+            if (path != null && !path.isEmpty() && path.charAt(0) != '/')
-                && ((path.length() > 0) && (path.charAt(0) != '/')))
+                throw new URISyntaxException(s, "Relative path in absolute URI");
-                throw new URISyntaxException(s,
-                                             "Relative path in absolute URI");
         }
     }
 
@@ -2163,7 +2161,7 @@ public final class URI
             ru.port = base.port;
 
             String cp = (child.path == null) ? "" : child.path;
-            if ((cp.length() > 0) && (cp.charAt(0) == '/')) {
+            if (!cp.isEmpty() && cp.charAt(0) == '/') {
                 // 5.2 (5): Child path is absolute
                 ru.path = child.path;
             } else {
@@ -2187,7 +2185,7 @@ public final class URI
     // o.w., return a new URI containing the normalized path.
     //
     private static URI normalize(URI u) {
-        if (u.isOpaque() || (u.path == null) || (u.path.length() == 0))
+        if (u.isOpaque() || u.path == null || u.path.isEmpty())
             return u;
 
         String np = normalize(u.path);

src/java.base/share/classes/java/net/URL.java

@@ -1513,7 +1513,7 @@ public final class URL implements java.io.Serializable {
         String ref = (String)gf.get("ref", null);
         int hashCode = gf.get("hashCode", -1);
         if (authority == null
-                && ((host != null && host.length() > 0) || port != -1)) {
+                && ((host != null && !host.isEmpty()) || port != -1)) {
             if (host == null)
                 host = "";
             authority = (port == -1) ? host : host + ":" + port;
@@ -1560,7 +1560,7 @@ public final class URL implements java.io.Serializable {
 
         // Construct authority part
         if (authority == null
-            && ((host != null && host.length() > 0) || port != -1)) {
+            && ((host != null && !host.isEmpty()) || port != -1)) {
             if (host == null)
                 host = "";
             authority = (port == -1) ? host : host + ":" + port;
@@ -1716,7 +1716,7 @@ final class UrlDeserializedState {
 
         // pre-compute length of StringBuffer
         int len = protocol.length() + 1;
-        if (authority != null && authority.length() > 0)
+        if (authority != null && !authority.isEmpty())
             len += 2 + authority.length();
         if (file != null) {
             len += file.length();
@@ -1726,7 +1726,7 @@ final class UrlDeserializedState {
         StringBuilder result = new StringBuilder(len);
         result.append(protocol);
         result.append(":");
-        if (authority != null && authority.length() > 0) {
+        if (authority != null && !authority.isEmpty()) {
             result.append("//");
             result.append(authority);
         }

src/java.base/share/classes/java/net/URLClassLoader.java

@@ -743,7 +743,7 @@ public class URLClassLoader extends SecureClassLoader implements Closeable {
                 locUrl = ((JarURLConnection)urlConnection).getJarFileURL();
             }
             String host = locUrl.getHost();
-            if (host != null && (host.length() > 0))
+            if (host != null && !host.isEmpty())
                 p = new SocketPermission(host,
                                          SecurityConstants.SOCKET_CONNECT_ACCEPT_ACTION);
         }

src/java.base/share/classes/java/net/URLDecoder.java

@@ -133,7 +133,7 @@ public class URLDecoder {
      * @since 1.4
      */
     public static String decode(String s, String enc) throws UnsupportedEncodingException {
-        if (enc.length() == 0) {
+        if (enc.isEmpty()) {
             throw new UnsupportedEncodingException ("URLDecoder: empty string enc parameter");
         }
 

src/java.base/share/classes/java/net/URLPermission.java

@@ -409,7 +409,7 @@ public final class URLPermission extends Permission {
             char c = methods.charAt(i);
             if (c == ',') {
                 String s = b.toString();
-                if (s.length() > 0)
+                if (!s.isEmpty())
                     l.add(s);
                 b = new StringBuilder();
             } else if (c == ' ' || c == '\t') {
@@ -423,7 +423,7 @@ public final class URLPermission extends Permission {
             }
         }
         String s = b.toString();
-        if (s.length() > 0)
+        if (!s.isEmpty())
             l.add(s);
         return l;
     }
@@ -448,7 +448,7 @@ public final class URLPermission extends Permission {
                 b.append(c);
             } else if (c == ',') {
                 String s = b.toString();
-                if (s.length() > 0)
+                if (!s.isEmpty())
                     l.add(s);
                 b = new StringBuilder();
                 capitalizeNext = true;
@@ -458,7 +458,7 @@ public final class URLPermission extends Permission {
             }
         }
         String s = b.toString();
-        if (s.length() > 0)
+        if (!s.isEmpty())
             l.add(s);
         return l;
     }

src/java.base/share/classes/java/net/URLStreamHandler.java

@@ -235,7 +235,7 @@ public abstract class URLStreamHandler {
             start = i;
             // If the authority is defined then the path is defined by the
             // spec only; See RFC 2396 Section 5.2.4.
-            if (authority != null && authority.length() > 0)
+            if (authority != null && !authority.isEmpty())
                 path = "";
         }
 
@@ -247,7 +247,7 @@ public abstract class URLStreamHandler {
         if (start < limit) {
             if (spec.charAt(start) == '/') {
                 path = spec.substring(start, limit);
-            } else if (path != null && path.length() > 0) {
+            } else if (path != null && !path.isEmpty()) {
                 isRelPath = true;
                 int ind = path.lastIndexOf('/');
                 String separator = "";
@@ -483,11 +483,11 @@ public abstract class URLStreamHandler {
         String s;
         return u.getProtocol()
             + ':'
-            + (((s = u.getAuthority()) != null && s.length() > 0)
+            + ((s = u.getAuthority()) != null && !s.isEmpty()
                ? "//" + s : "")
-            + (((s = u.getPath()) != null) ? s : "")
+            + ((s = u.getPath()) != null ? s : "")
-            + (((s = u.getQuery()) != null) ? '?' + s : "")
+            + ((s = u.getQuery()) != null ? '?' + s : "")
-            + (((s = u.getRef()) != null) ? '#' + s : "");
+            + ((s = u.getRef()) != null ? '#' + s : "");
     }
 
     /**
@@ -544,7 +544,7 @@ public abstract class URLStreamHandler {
          */
         String authority = null;
         String userInfo = null;
-        if (host != null && host.length() != 0) {
+        if (host != null && !host.isEmpty()) {
             authority = (port == -1) ? host : host + ":" + port;
             int at = host.lastIndexOf('@');
             if (at != -1) {

src/java.base/share/classes/java/nio/file/LinkPermission.java

@@ -104,7 +104,7 @@ public final class LinkPermission extends BasicPermission {
     public LinkPermission(String name, String actions) {
         super(name);
         checkName(name);
-        if (actions != null && actions.length() > 0) {
+        if (actions != null && !actions.isEmpty()) {
             throw new IllegalArgumentException("actions: " + actions);
         }
     }

src/java.base/share/classes/java/security/AlgorithmParameterGenerator.java

@@ -228,7 +228,7 @@ public class AlgorithmParameterGenerator {
         throws NoSuchAlgorithmException, NoSuchProviderException
     {
         Objects.requireNonNull(algorithm, "null algorithm name");
-        if (provider == null || provider.length() == 0)
+        if (provider == null || provider.isEmpty())
             throw new IllegalArgumentException("missing provider");
         Object[] objs = Security.getImpl(algorithm,
                                          "AlgorithmParameterGenerator",

src/java.base/share/classes/java/security/AlgorithmParameters.java

@@ -209,7 +209,7 @@ public class AlgorithmParameters {
         throws NoSuchAlgorithmException, NoSuchProviderException
     {
         Objects.requireNonNull(algorithm, "null algorithm name");
-        if (provider == null || provider.length() == 0)
+        if (provider == null || provider.isEmpty())
             throw new IllegalArgumentException("missing provider");
         Object[] objs = Security.getImpl(algorithm, "AlgorithmParameters",
                                          provider);

src/java.base/share/classes/java/security/KeyStore.java

@@ -913,7 +913,7 @@ public class KeyStore {
         throws KeyStoreException, NoSuchProviderException
     {
         Objects.requireNonNull(type, "null type name");
-        if (provider == null || provider.length() == 0)
+        if (provider == null || provider.isEmpty())
             throw new IllegalArgumentException("missing provider");
         try {
             Object[] objs = Security.getImpl(type, "KeyStore", provider);

src/java.base/share/classes/java/security/MessageDigest.java

@@ -237,7 +237,7 @@ public abstract class MessageDigest extends MessageDigestSpi {
         throws NoSuchAlgorithmException, NoSuchProviderException
     {
         Objects.requireNonNull(algorithm, "null algorithm name");
-        if (provider == null || provider.length() == 0)
+        if (provider == null || provider.isEmpty())
             throw new IllegalArgumentException("missing provider");
         Object[] objs = Security.getImpl(algorithm, "MessageDigest", provider);
         if (objs[0] instanceof MessageDigest) {

src/java.base/share/classes/java/security/Permission.java

@@ -222,7 +222,7 @@ public abstract class Permission implements Guard, java.io.Serializable {
      */
     public String toString() {
         String actions = getActions();
-        if ((actions == null) || (actions.length() == 0)) { // OPTIONAL
+        if (actions == null || actions.isEmpty()) { // OPTIONAL
             return "(\"" + getClass().getName() + "\" \"" + name + "\")";
         } else {
             return "(\"" + getClass().getName() + "\" \"" + name +

src/java.base/share/classes/java/security/Policy.java

@@ -456,7 +456,7 @@ public abstract class Policy {
                 throws NoSuchProviderException, NoSuchAlgorithmException {
 
         Objects.requireNonNull(type, "null type name");
-        if (provider == null || provider.length() == 0) {
+        if (provider == null || provider.isEmpty()) {
             throw new IllegalArgumentException("missing provider");
         }
 

src/java.base/share/classes/java/security/SecureRandom.java

@@ -942,7 +942,7 @@ public class SecureRandom extends java.util.Random {
                 }
             });
 
-        if ((property == null) || (property.length() == 0)) {
+        if (property == null || property.isEmpty()) {
             throw new NoSuchAlgorithmException(
                 "Null/empty securerandom.strongAlgorithms Security Property");
         }

src/java.base/share/classes/java/security/Security.java

@@ -649,7 +649,7 @@ public final class Security {
             }
         }
 
-        if ((candidates == null) || (candidates.isEmpty()))
+        if (candidates == null || candidates.isEmpty())
             return null;
 
         Object[] candidatesArray = candidates.toArray();
@@ -1005,11 +1005,11 @@ public final class Security {
         String algName = null;
         String attrName = null;
 
-        if (filterValue.length() == 0) {
+        if (filterValue.isEmpty()) {
             // The filterValue is an empty string. So the filterKey
             // should be in the format of <crypto_service>.<algorithm_or_type>.
             algName = filterKey.substring(algIndex + 1).trim();
-            if (algName.length() == 0) {
+            if (algName.isEmpty()) {
                 // There must be a algorithm or type name.
                 throw new InvalidParameterException("Invalid filter");
             }
@@ -1024,7 +1024,7 @@ public final class Security {
                 throw new InvalidParameterException("Invalid filter");
             } else {
                 attrName = filterKey.substring(attrIndex + 1).trim();
-                if (attrName.length() == 0) {
+                if (attrName.isEmpty()) {
                     // There is no attribute name in the filter.
                     throw new InvalidParameterException("Invalid filter");
                 }
@@ -1070,7 +1070,7 @@ public final class Security {
      **/
     public static Set<String> getAlgorithms(String serviceName) {
 
-        if ((serviceName == null) || (serviceName.length() == 0) ||
+        if ((serviceName == null) || (serviceName.isEmpty()) ||
             (serviceName.endsWith("."))) {
             return Collections.emptySet();
         }

src/java.base/share/classes/java/security/Signature.java

@@ -360,7 +360,7 @@ public abstract class Signature extends SignatureSpi {
         Objects.requireNonNull(algorithm, "null algorithm name");
         if (algorithm.equalsIgnoreCase(RSA_SIGNATURE)) {
             // exception compatibility with existing code
-            if ((provider == null) || (provider.length() == 0)) {
+            if (provider == null || provider.isEmpty()) {
                 throw new IllegalArgumentException("missing provider");
             }
             Provider p = Security.getProvider(provider);

src/java.base/share/classes/java/security/cert/TrustAnchor.java

@@ -210,7 +210,7 @@ public class TrustAnchor {
         if (caName == null)
             throw new NullPointerException("the caName parameter must be " +
                 "non-null");
-        if (caName.length() == 0)
+        if (caName.isEmpty())
             throw new IllegalArgumentException("the caName " +
                 "parameter must be a non-empty String");
         // check if caName is formatted correctly

src/java.base/share/classes/java/text/AttributedString.java

@@ -85,7 +85,7 @@ public class AttributedString {
 
             text = buffer.toString();
 
-            if (text.length() > 0) {
+            if (!text.isEmpty()) {
                 // Determine the runs, creating a new run when the attributes
                 // differ.
                 int offset = 0;
@@ -144,7 +144,7 @@ public class AttributedString {
         }
         this.text = text;
 
-        if (text.length() == 0) {
+        if (text.isEmpty()) {
             if (attributes.isEmpty())
                 return;
             throw new IllegalArgumentException("Can't add attribute to 0-length text");

src/java.base/share/classes/java/text/CollationElementIterator.java

@@ -125,7 +125,7 @@ public final class CollationElementIterator
     CollationElementIterator(String sourceText, RuleBasedCollator owner) {
         this.owner = owner;
         ordering = owner.getTables();
-        if ( sourceText.length() != 0 ) {
+        if (!sourceText.isEmpty()) {
             NormalizerBase.Mode mode =
                 CollatorUtilities.toNormalizerMode(owner.getDecomposition());
             text = new NormalizerBase(sourceText, mode);

src/java.base/share/classes/java/text/CompactNumberFormat.java

@@ -799,7 +799,7 @@ public final class CompactNumberFormat extends NumberFormat {
      */
     private void append(StringBuffer result, String string,
             FieldDelegate delegate, List<FieldPosition> positions) {
-        if (string.length() > 0) {
+        if (!string.isEmpty()) {
             int start = result.length();
             result.append(string);
             for (int counter = 0; counter < positions.size(); counter++) {
@@ -1213,7 +1213,7 @@ public final class CompactNumberFormat extends NumberFormat {
         }
 
         // If no 0s are specified in a non empty pattern, it is invalid
-        if (pattern.length() != 0 && zeros.isEmpty()) {
+        if (!pattern.isEmpty() && zeros.isEmpty()) {
             throw new IllegalArgumentException("Invalid pattern"
                     + " [" + pattern + "]: all patterns must include digit"
                     + " placement 0s");

src/java.base/share/classes/java/text/DecimalFormat.java

@@ -1113,11 +1113,9 @@ public class DecimalFormat extends NumberFormat {
 
             // Records the need for adding prefix or suffix
             fastPathData.positiveAffixesRequired
-                    = (positivePrefix.length() != 0)
+                    = !positivePrefix.isEmpty() || !positiveSuffix.isEmpty();
-                        || (positiveSuffix.length() != 0);
             fastPathData.negativeAffixesRequired
-                    = (negativePrefix.length() != 0)
+                    = !negativePrefix.isEmpty() || !negativeSuffix.isEmpty();
-                        || (negativeSuffix.length() != 0);
 
             // Creates a cached char container for result, with max possible size.
             int maxNbIntegralDigits = 10;
@@ -2062,7 +2060,7 @@ public class DecimalFormat extends NumberFormat {
                         Format.Field signAttribute) {
         int start = result.length();
 
-        if (string.length() > 0) {
+        if (!string.isEmpty()) {
             result.append(string);
             for (int counter = 0, max = positions.length; counter < max;
                  counter++) {
@@ -3042,7 +3040,7 @@ public class DecimalFormat extends NumberFormat {
                     } else {
                         string = symbols.getCurrencySymbol();
                     }
-                    if (string.length() > 0) {
+                    if (!string.isEmpty()) {
                         if (positions == null) {
                             positions = new ArrayList<>(2);
                         }
@@ -3613,7 +3611,7 @@ public class DecimalFormat extends NumberFormat {
             }
         }
 
-        if (pattern.length() == 0) {
+        if (pattern.isEmpty()) {
             posPrefixPattern = posSuffixPattern = "";
             setMinimumIntegerDigits(0);
             setMaximumIntegerDigits(MAXIMUM_INTEGER_DIGITS);

src/java.base/share/classes/java/text/DecimalFormatSymbols.java

@@ -663,7 +663,7 @@ public class DecimalFormatSymbols implements Cloneable, Serializable {
         // Check for empty country string separately because it's a valid
         // country ID for Locale (and used for the C locale), but not a valid
         // ISO 3166 country code, and exceptions are expensive.
-        if (locale.getCountry().length() > 0) {
+        if (!locale.getCountry().isEmpty()) {
             try {
                 currency = Currency.getInstance(locale);
             } catch (IllegalArgumentException e) {

src/java.base/share/classes/java/text/MergeCollation.java

@@ -92,7 +92,7 @@ final class MergeCollation {
         int i;
         for (i = 0; i < patterns.size(); ++i) {
             PatternEntry entry = patterns.get(i);
-            if (entry.extension.length() != 0) {
+            if (!entry.extension.isEmpty()) {
                 if (extList == null)
                     extList = new ArrayList<>();
                 extList.add(entry);
@@ -122,7 +122,7 @@ final class MergeCollation {
     private final PatternEntry findLastWithNoExtension(int i) {
         for (--i;i >= 0; --i) {
             PatternEntry entry = patterns.get(i);
-            if (entry.extension.length() == 0) {
+            if (entry.extension.isEmpty()) {
                 return entry;
             }
         }

src/java.base/share/classes/java/text/MessageFormat.java

@@ -1330,7 +1330,7 @@ public class MessageFormat extends Format {
                         }
                         arg = null;
                     }
-                    if (arg != null && arg.length() > 0) {
+                    if (arg != null && !arg.isEmpty()) {
                         result.append(arg);
                         characterIterators.add(
                                  createAttributedCharacterIterator(
@@ -1476,7 +1476,7 @@ public class MessageFormat extends Format {
 
         // now get the format
         Format newFormat = null;
-        if (segments[SEG_TYPE].length() != 0) {
+        if (!segments[SEG_TYPE].isEmpty()) {
             int type = findKeyword(segments[SEG_TYPE], TYPE_KEYWORDS);
             switch (type) {
             case TYPE_NULL:

src/java.base/share/classes/java/text/PatternEntry.java

@@ -141,7 +141,7 @@ class PatternEntry {
         if (showWhiteSpace)
             toAddTo.append(' ');
         appendQuoted(chars,toAddTo);
-        if (showExtension && extension.length() != 0) {
+        if (showExtension && !extension.isEmpty()) {
             toAddTo.append('/');
             appendQuoted(extension,toAddTo);
         }

src/java.base/share/classes/java/text/RBTableBuilder.java

@@ -75,13 +75,10 @@ final class RBTableBuilder {
      * @exception ParseException If the rules format is incorrect.
      */
 
-    public void build(String pattern, int decmp) throws ParseException
+    public void build(String pattern, int decmp) throws ParseException {
-    {
-        boolean isSource = true;
-        int i = 0;
         String expChars;
         String groupChars;
-        if (pattern.length() == 0)
+        if (pattern.isEmpty())
             throw new ParseException("Build rules empty.", 0);
 
         // This array maps Unicode characters to their collation ordering
@@ -119,8 +116,7 @@ final class RBTableBuilder {
         int order = 0;
 
         // Now walk though each entry and add it to my own tables
-        for (i = 0; i < mPattern.getCount(); ++i)
+        for (int i = 0; i < mPattern.getCount(); ++i) {
-        {
             PatternEntry entry = mPattern.getItemAt(i);
             if (entry != null) {
                 groupChars = entry.getChars();
@@ -140,7 +136,7 @@ final class RBTableBuilder {
                 order = increment(entry.getStrength(), order);
                 expChars = entry.getExtension();
 
-                if (expChars.length() != 0) {
+                if (!expChars.isEmpty()) {
                     addExpandOrder(groupChars, expChars, order);
                 } else if (groupChars.length() > 1) {
                     char ch = groupChars.charAt(0);

src/java.base/share/classes/java/time/ZoneId.java

@@ -372,7 +372,7 @@ public abstract class ZoneId implements Serializable {
     public static ZoneId ofOffset(String prefix, ZoneOffset offset) {
         Objects.requireNonNull(prefix, "prefix");
         Objects.requireNonNull(offset, "offset");
-        if (prefix.length() == 0) {
+        if (prefix.isEmpty()) {
             return offset;
         }
 

src/java.base/share/classes/java/time/format/DateTimeFormatterBuilder.java

@@ -1439,7 +1439,7 @@ public final class DateTimeFormatterBuilder {
      */
     public DateTimeFormatterBuilder appendLiteral(String literal) {
         Objects.requireNonNull(literal, "literal");
-        if (literal.length() > 0) {
+        if (!literal.isEmpty()) {
             if (literal.length() == 1) {
                 appendInternal(new CharLiteralPrinterParser(literal.charAt(0)));
             } else {
@@ -1832,7 +1832,7 @@ public final class DateTimeFormatterBuilder {
                     throw new IllegalArgumentException("Pattern ends with an incomplete string literal: " + pattern);
                 }
                 String str = pattern.substring(start + 1, pos);
-                if (str.length() == 0) {
+                if (str.isEmpty()) {
                     appendLiteral('\'');
                 } else {
                     appendLiteral(str.replace("''", "'"));
@@ -4332,7 +4332,7 @@ public final class DateTimeFormatterBuilder {
             this.key = k;
             this.value = v;
             this.child = child;
-            if (k.length() == 0){
+            if (k.isEmpty()) {
                 c0 = 0xffff;
             } else {
                 c0 = key.charAt(0);

src/java.base/share/classes/java/util/Calendar.java

@@ -2232,7 +2232,7 @@ public abstract class Calendar implements Serializable, Cloneable, Comparable<Ca
         if (strings != null) {
             Map<String,Integer> names = new HashMap<>();
             for (int i = 0; i < strings.length; i++) {
-                if (strings[i].length() == 0) {
+                if (strings[i].isEmpty()) {
                     continue;
                 }
                 names.put(strings[i], i);

src/java.base/share/classes/java/util/Locale.java

@@ -1396,11 +1396,11 @@ public final class Locale implements Cloneable, Serializable {
      */
     @Override
     public final String toString() {
-        boolean l = (baseLocale.getLanguage().length() != 0);
+        boolean l = !baseLocale.getLanguage().isEmpty();
-        boolean s = (baseLocale.getScript().length() != 0);
+        boolean s = !baseLocale.getScript().isEmpty();
-        boolean r = (baseLocale.getRegion().length() != 0);
+        boolean r = !baseLocale.getRegion().isEmpty();
-        boolean v = (baseLocale.getVariant().length() != 0);
+        boolean v = !baseLocale.getVariant().isEmpty();
-        boolean e = (localeExtensions != null && localeExtensions.getID().length() != 0);
+        boolean e = localeExtensions != null && !localeExtensions.getID().isEmpty();
 
         StringBuilder result = new StringBuilder(baseLocale.getLanguage());
         if (r || (l && (v || s || e))) {
@@ -1504,18 +1504,18 @@ public final class Locale implements Cloneable, Serializable {
         StringBuilder buf = new StringBuilder();
 
         String subtag = tag.getLanguage();
-        if (subtag.length() > 0) {
+        if (!subtag.isEmpty()) {
             buf.append(LanguageTag.canonicalizeLanguage(subtag));
         }
 
         subtag = tag.getScript();
-        if (subtag.length() > 0) {
+        if (!subtag.isEmpty()) {
             buf.append(LanguageTag.SEP);
             buf.append(LanguageTag.canonicalizeScript(subtag));
         }
 
         subtag = tag.getRegion();
-        if (subtag.length() > 0) {
+        if (!subtag.isEmpty()) {
             buf.append(LanguageTag.SEP);
             buf.append(LanguageTag.canonicalizeRegion(subtag));
         }
@@ -1534,7 +1534,7 @@ public final class Locale implements Cloneable, Serializable {
         }
 
         subtag = tag.getPrivateuse();
-        if (subtag.length() > 0) {
+        if (!subtag.isEmpty()) {
             if (buf.length() > 0) {
                 buf.append(LanguageTag.SEP);
             }
@@ -1684,7 +1684,7 @@ public final class Locale implements Cloneable, Serializable {
         bldr.setLanguageTag(tag);
         BaseLocale base = bldr.getBaseLocale();
         LocaleExtensions exts = bldr.getLocaleExtensions();
-        if (exts == null && base.getVariant().length() > 0) {
+        if (exts == null && !base.getVariant().isEmpty()) {
             exts = getCompatibilityExtensions(base.getLanguage(), base.getScript(),
                                               base.getRegion(), base.getVariant());
         }
@@ -1917,7 +1917,7 @@ public final class Locale implements Cloneable, Serializable {
      * @exception NullPointerException if <code>inLocale</code> is <code>null</code>
      */
     public String getDisplayVariant(Locale inLocale) {
-        if (baseLocale.getVariant().length() == 0)
+        if (baseLocale.getVariant().isEmpty())
             return "";
 
         LocaleResources lr = LocaleProviderAdapter
@@ -1998,14 +1998,14 @@ public final class Locale implements Cloneable, Serializable {
         // The display name consists of a main name, followed by qualifiers.
         // Typically, the format is "MainName (Qualifier, Qualifier)" but this
         // depends on what pattern is stored in the display locale.
-        String   mainName       = null;
+        String   mainName;
-        String[] qualifierNames = null;
+        String[] qualifierNames;
 
         // The main name is the language, or if there is no language, the script,
         // then if no script, the country. If there is no language/script/country
         // (an anomalous situation) then the display name is simply the variant's
         // display name.
-        if (languageName.length() == 0 && scriptName.length() == 0 && countryName.length() == 0) {
+        if (languageName.isEmpty() && scriptName.isEmpty() && countryName.isEmpty()) {
             if (variantNames.length == 0) {
                 return "";
             } else {
@@ -2013,13 +2013,13 @@ public final class Locale implements Cloneable, Serializable {
             }
         }
         ArrayList<String> names = new ArrayList<>(4);
-        if (languageName.length() != 0) {
+        if (!languageName.isEmpty()) {
             names.add(languageName);
         }
-        if (scriptName.length() != 0) {
+        if (!scriptName.isEmpty()) {
             names.add(scriptName);
         }
-        if (countryName.length() != 0) {
+        if (!countryName.isEmpty()) {
             names.add(countryName);
         }
         if (variantNames.length != 0) {
@@ -2309,7 +2309,7 @@ public final class Locale implements Cloneable, Serializable {
         String variant = (String)fields.get("variant", "");
         String extStr = (String)fields.get("extensions", "");
         baseLocale = BaseLocale.getInstance(convertOldISOCodes(language), script, country, variant);
-        if (extStr.length() > 0) {
+        if (!extStr.isEmpty()) {
             try {
                 InternalLocaleBuilder bldr = new InternalLocaleBuilder();
                 bldr.setExtensions(extStr);
@@ -2367,13 +2367,13 @@ public final class Locale implements Cloneable, Serializable {
         LocaleExtensions extensions = null;
         // Special cases for backward compatibility support
         if (LocaleUtils.caseIgnoreMatch(language, "ja")
-                && script.length() == 0
+                && script.isEmpty()
                 && LocaleUtils.caseIgnoreMatch(country, "jp")
                 && "JP".equals(variant)) {
             // ja_JP_JP -> u-ca-japanese (calendar = japanese)
             extensions = LocaleExtensions.CALENDAR_JAPANESE;
         } else if (LocaleUtils.caseIgnoreMatch(language, "th")
-                && script.length() == 0
+                && script.isEmpty()
                 && LocaleUtils.caseIgnoreMatch(country, "th")
                 && "TH".equals(variant)) {
             // th_TH_TH -> u-nu-thai (numbersystem = thai)
@@ -2806,7 +2806,7 @@ public final class Locale implements Cloneable, Serializable {
         public Locale build() {
             BaseLocale baseloc = localeBuilder.getBaseLocale();
             LocaleExtensions extensions = localeBuilder.getLocaleExtensions();
-            if (extensions == null && baseloc.getVariant().length() > 0) {
+            if (extensions == null && !baseloc.getVariant().isEmpty()) {
                 extensions = getCompatibilityExtensions(baseloc.getLanguage(), baseloc.getScript(),
                         baseloc.getRegion(), baseloc.getVariant());
             }

src/java.base/share/classes/java/util/ResourceBundle.java

@@ -771,8 +771,8 @@ public abstract class ResourceBundle {
         @Override
         public String toString() {
             String l = locale.toString();
-            if (l.length() == 0) {
+            if (l.isEmpty()) {
-                if (locale.getVariant().length() != 0) {
+                if (!locale.getVariant().isEmpty()) {
                     l = "__" + locale.getVariant();
                 } else {
                     l = "\"\"";
@@ -2903,7 +2903,7 @@ public abstract class ResourceBundle {
                     List<Locale> bokmalList = new LinkedList<>();
                     for (Locale l : tmpList) {
                         bokmalList.add(l);
-                        if (l.getLanguage().length() == 0) {
+                        if (l.getLanguage().isEmpty()) {
                             break;
                         }
                         bokmalList.add(Locale.getInstance("no", l.getScript(), l.getCountry(),
@@ -2921,7 +2921,7 @@ public abstract class ResourceBundle {
                 }
                 // Special handling for Chinese
                 else if (language.equals("zh")) {
-                    if (script.length() == 0 && region.length() > 0) {
+                    if (script.isEmpty() && !region.isEmpty()) {
                         // Supply script for users who want to use zh_Hans/zh_Hant
                         // as bundle names (recommended for Java7+)
                         switch (region) {
@@ -2944,7 +2944,7 @@ public abstract class ResourceBundle {
             private static List<Locale> getDefaultList(String language, String script, String region, String variant) {
                 List<String> variants = null;
 
-                if (variant.length() > 0) {
+                if (!variant.isEmpty()) {
                     variants = new LinkedList<>();
                     int idx = variant.length();
                     while (idx != -1) {
@@ -2960,14 +2960,14 @@ public abstract class ResourceBundle {
                         list.add(Locale.getInstance(language, script, region, v, null));
                     }
                 }
-                if (region.length() > 0) {
+                if (!region.isEmpty()) {
                     list.add(Locale.getInstance(language, script, region, "", null));
                 }
-                if (script.length() > 0) {
+                if (!script.isEmpty()) {
                     list.add(Locale.getInstance(language, script, "", "", null));
                     // Special handling for Chinese
                     if (language.equals("zh")) {
-                        if (region.length() == 0) {
+                        if (region.isEmpty()) {
                             // Supply region(country) for users who still package Chinese
                             // bundles using old convension.
                             switch (script) {
@@ -2988,11 +2988,11 @@ public abstract class ResourceBundle {
                             list.add(Locale.getInstance(language, "", region, v, null));
                         }
                     }
-                    if (region.length() > 0) {
+                    if (!region.isEmpty()) {
                         list.add(Locale.getInstance(language, "", region, "", null));
                     }
                 }
-                if (language.length() > 0) {
+                if (!language.isEmpty()) {
                     list.add(Locale.getInstance(language, "", "", "", null));
                 }
                 // Add root locale at the end

src/java.base/share/classes/java/util/Scanner.java

@@ -1297,16 +1297,16 @@ public final class Scanner implements Iterator<String>, Closeable {
         nanString = "\\Q" + dfs.getNaN() + "\\E";
         infinityString = "\\Q" + dfs.getInfinity() + "\\E";
         positivePrefix = df.getPositivePrefix();
-        if (positivePrefix.length() > 0)
+        if (!positivePrefix.isEmpty())
             positivePrefix = "\\Q" + positivePrefix + "\\E";
         negativePrefix = df.getNegativePrefix();
-        if (negativePrefix.length() > 0)
+        if (!negativePrefix.isEmpty())
             negativePrefix = "\\Q" + negativePrefix + "\\E";
         positiveSuffix = df.getPositiveSuffix();
-        if (positiveSuffix.length() > 0)
+        if (!positiveSuffix.isEmpty())
             positiveSuffix = "\\Q" + positiveSuffix + "\\E";
         negativeSuffix = df.getNegativeSuffix();
-        if (negativeSuffix.length() > 0)
+        if (!negativeSuffix.isEmpty())
             negativeSuffix = "\\Q" + negativeSuffix + "\\E";
 
         // Force rebuilding and recompilation of locale dependent

src/java.base/share/classes/java/util/regex/Pattern.java

@@ -1390,7 +1390,7 @@ public final class Pattern
         localTCNCount = 0;
 
         // if length > 0, the Pattern is lazily compiled
-        if (pattern.length() == 0) {
+        if (pattern.isEmpty()) {
             root = new Start(lastAccept);
             matchRoot = lastAccept;
             compiled = true;
@@ -1423,7 +1423,7 @@ public final class Pattern
         localCount = 0;
         localTCNCount = 0;
 
-        if (pattern.length() > 0) {
+        if (!pattern.isEmpty()) {
             compile();
         } else {
             root = new Start(lastAccept);

src/java.base/share/classes/javax/crypto/Cipher.java

@@ -341,7 +341,7 @@ public class Cipher {
             throw new NoSuchAlgorithmException("Invalid transformation " +
                                            "format:" + transformation);
         }
-        if ((parts[0] == null) || (parts[0].length() == 0)) {
+        if ((parts[0] == null) || (parts[0].isEmpty())) {
             throw new NoSuchAlgorithmException("Invalid transformation:" +
                                    "algorithm not specified-"
                                    + transformation);
@@ -445,10 +445,10 @@ public class Cipher {
         String alg = parts[0];
         String mode = parts[1];
         String pad = parts[2];
-        if ((mode != null) && (mode.length() == 0)) {
+        if ((mode != null) && (mode.isEmpty())) {
             mode = null;
         }
-        if ((pad != null) && (pad.length() == 0)) {
+        if ((pad != null) && (pad.isEmpty())) {
             pad = null;
         }
 
@@ -634,7 +634,7 @@ public class Cipher {
         if ((transformation == null) || transformation.isEmpty()) {
             throw new NoSuchAlgorithmException("Null or empty transformation");
         }
-        if ((provider == null) || (provider.length() == 0)) {
+        if ((provider == null) || (provider.isEmpty())) {
             throw new IllegalArgumentException("Missing provider");
         }
         Provider p = Security.getProvider(provider);

src/java.base/share/classes/javax/crypto/SealedObject.java

@@ -337,7 +337,7 @@ public class SealedObject implements Serializable {
         if (key == null) {
             throw new NullPointerException("key is null");
         }
-        if (provider == null || provider.length() == 0) {
+        if (provider == null || provider.isEmpty()) {
             throw new IllegalArgumentException("missing provider");
         }
 

src/java.base/share/classes/javax/net/ssl/SSLSocketFactory.java

@@ -133,7 +133,7 @@ public abstract class SSLSocketFactory extends SocketFactory
                 String s = java.security.Security.getProperty(name);
                 if (s != null) {
                     s = s.trim();
-                    if (s.length() == 0) {
+                    if (s.isEmpty()) {
                         s = null;
                     }
                 }

src/java.base/share/classes/javax/security/auth/PrivateCredentialPermission.java

@@ -312,7 +312,7 @@ public final class PrivateCredentialPermission extends Permission {
 
     private void init(String name) {
 
-        if (name == null || name.trim().length() == 0) {
+        if (name == null || name.trim().isEmpty()) {
             throw new IllegalArgumentException("invalid empty name");
         }
 

src/java.base/share/classes/javax/security/auth/callback/ChoiceCallback.java

@@ -98,13 +98,13 @@ public class ChoiceCallback implements Callback, java.io.Serializable {
     public ChoiceCallback(String prompt, String[] choices,
                 int defaultChoice, boolean multipleSelectionsAllowed) {
 
-        if (prompt == null || prompt.length() == 0 ||
+        if (prompt == null || prompt.isEmpty() ||
             choices == null || choices.length == 0 ||
             defaultChoice < 0 || defaultChoice >= choices.length)
             throw new IllegalArgumentException();
 
         for (int i = 0; i < choices.length; i++) {
-            if (choices[i] == null || choices[i].length() == 0)
+            if (choices[i] == null || choices[i].isEmpty())
                 throw new IllegalArgumentException();
         }
 

src/java.base/share/classes/javax/security/auth/callback/ConfirmationCallback.java

@@ -248,7 +248,7 @@ public class ConfirmationCallback implements Callback, java.io.Serializable {
             throw new IllegalArgumentException();
 
         for (int i = 0; i < options.length; i++) {
-            if (options[i] == null || options[i].length() == 0)
+            if (options[i] == null || options[i].isEmpty())
                 throw new IllegalArgumentException();
         }
 
@@ -294,7 +294,7 @@ public class ConfirmationCallback implements Callback, java.io.Serializable {
     public ConfirmationCallback(String prompt, int messageType,
                 int optionType, int defaultOption) {
 
-        if (prompt == null || prompt.length() == 0 ||
+        if (prompt == null || prompt.isEmpty() ||
             messageType < INFORMATION || messageType > ERROR ||
             optionType < YES_NO_OPTION || optionType > OK_CANCEL_OPTION)
             throw new IllegalArgumentException();
@@ -357,14 +357,14 @@ public class ConfirmationCallback implements Callback, java.io.Serializable {
     public ConfirmationCallback(String prompt, int messageType,
                 String[] options, int defaultOption) {
 
-        if (prompt == null || prompt.length() == 0 ||
+        if (prompt == null || prompt.isEmpty() ||
             messageType < INFORMATION || messageType > ERROR ||
             options == null || options.length == 0 ||
             defaultOption < 0 || defaultOption >= options.length)
             throw new IllegalArgumentException();
 
         for (int i = 0; i < options.length; i++) {
-            if (options[i] == null || options[i].length() == 0)
+            if (options[i] == null || options[i].isEmpty())
                 throw new IllegalArgumentException();
         }
 

src/java.base/share/classes/javax/security/auth/callback/NameCallback.java

@@ -62,7 +62,7 @@ public class NameCallback implements Callback, java.io.Serializable {
      *                  or if {@code prompt} has a length of 0.
      */
     public NameCallback(String prompt) {
-        if (prompt == null || prompt.length() == 0)
+        if (prompt == null || prompt.isEmpty())
             throw new IllegalArgumentException();
         this.prompt = prompt;
     }
@@ -82,8 +82,8 @@ public class NameCallback implements Callback, java.io.Serializable {
      *                  or if {@code defaultName} has a length of 0.
      */
     public NameCallback(String prompt, String defaultName) {
-        if (prompt == null || prompt.length() == 0 ||
+        if (prompt == null || prompt.isEmpty() ||
-            defaultName == null || defaultName.length() == 0)
+            defaultName == null || defaultName.isEmpty())
             throw new IllegalArgumentException();
 
         this.prompt = prompt;

src/java.base/share/classes/javax/security/auth/callback/PasswordCallback.java

@@ -67,7 +67,7 @@ public class PasswordCallback implements Callback, java.io.Serializable {
      *                  if {@code prompt} has a length of 0.
      */
     public PasswordCallback(String prompt, boolean echoOn) {
-        if (prompt == null || prompt.length() == 0)
+        if (prompt == null || prompt.isEmpty())
             throw new IllegalArgumentException();
 
         this.prompt = prompt;

src/java.base/share/classes/javax/security/auth/callback/TextInputCallback.java

@@ -63,7 +63,7 @@ public class TextInputCallback implements Callback, java.io.Serializable {
      *                  or if {@code prompt} has a length of 0.
      */
     public TextInputCallback(String prompt) {
-        if (prompt == null || prompt.length() == 0)
+        if (prompt == null || prompt.isEmpty())
             throw new IllegalArgumentException();
         this.prompt = prompt;
     }
@@ -83,8 +83,8 @@ public class TextInputCallback implements Callback, java.io.Serializable {
      *                  or if {@code defaultText} has a length of 0.
      */
     public TextInputCallback(String prompt, String defaultText) {
-        if (prompt == null || prompt.length() == 0 ||
+        if (prompt == null || prompt.isEmpty() ||
-            defaultText == null || defaultText.length() == 0)
+            defaultText == null || defaultText.isEmpty())
             throw new IllegalArgumentException();
 
         this.prompt = prompt;

src/java.base/share/classes/javax/security/auth/callback/TextOutputCallback.java

@@ -74,7 +74,7 @@ public class TextOutputCallback implements Callback, java.io.Serializable {
     public TextOutputCallback(int messageType, String message) {
         if ((messageType != INFORMATION &&
                 messageType != WARNING && messageType != ERROR) ||
-            message == null || message.length() == 0)
+            message == null || message.isEmpty())
             throw new IllegalArgumentException();
 
         this.messageType = messageType;

src/java.base/share/classes/javax/security/auth/login/AppConfigurationEntry.java

@@ -75,7 +75,7 @@ public class AppConfigurationEntry {
                                 LoginModuleControlFlag controlFlag,
                                 Map<String,?> options)
     {
-        if (loginModuleName == null || loginModuleName.length() == 0 ||
+        if (loginModuleName == null || loginModuleName.isEmpty() ||
             (controlFlag != LoginModuleControlFlag.REQUIRED &&
                 controlFlag != LoginModuleControlFlag.REQUISITE &&
                 controlFlag != LoginModuleControlFlag.SUFFICIENT &&

src/java.base/share/classes/javax/security/auth/login/Configuration.java

@@ -418,7 +418,7 @@ public abstract class Configuration {
                 throws NoSuchProviderException, NoSuchAlgorithmException {
 
         Objects.requireNonNull(type, "null type name");
-        if (provider == null || provider.length() == 0) {
+        if (provider == null || provider.isEmpty()) {
             throw new IllegalArgumentException("missing provider");
         }
 

src/java.base/share/classes/javax/security/auth/login/LoginContext.java

@@ -300,7 +300,7 @@ public class LoginContext {
                 public CallbackHandler run() throws Exception {
                     String defaultHandler = java.security.Security.getProperty
                         (DEFAULT_HANDLER);
-                    if (defaultHandler == null || defaultHandler.length() == 0)
+                    if (defaultHandler == null || defaultHandler.isEmpty())
                         return null;
                     Class<? extends CallbackHandler> c = Class.forName(
                             defaultHandler, true,

src/java.base/share/classes/javax/security/cert/X509Certificate.java

@@ -210,7 +210,7 @@ public abstract class X509Certificate extends Certificate {
          * under JDK1.1.
          */
         String className = X509Provider;
-        if (className == null || className.length() == 0) {
+        if (className == null || className.isEmpty()) {
             // shouldn't happen, but assume corrupted properties file
             // provide access to sun implementation
             className = "com.sun.security.cert.internal.x509.X509V1CertImpl";

src/java.base/share/classes/jdk/internal/jimage/decompressor/SignatureParser.java

@@ -60,7 +60,7 @@ public class SignatureParser {
             switch (c) {
                 case 'L': {
                     String pkg = arguments.get(arg_index);
-                    if(pkg.length() > 0) {
+                    if(!pkg.isEmpty()) {
                         out.append(pkg).append("/");
                     }
                     arg_index+=1;

src/java.base/share/classes/jdk/internal/jimage/decompressor/StringSharingDecompressor.java

@@ -168,7 +168,7 @@ public class StringSharingDecompressor implements ResourceDecompressor {
                 int index = indices.get(argIndex);
                 argIndex += 1;
                 String pkg = reader.getString(index);
-                if (pkg.length() > 0) {
+                if (!pkg.isEmpty()) {
                     pkg = pkg + "/";
                     byte[] encoded = getEncoded(pkg);
                     buffer = safeAdd(buffer, encoded);

src/java.base/share/classes/jdk/internal/jrtfs/JrtFileSystem.java

@@ -123,7 +123,7 @@ class JrtFileSystem extends FileSystem {
         StringBuilder sb = new StringBuilder();
         sb.append(first);
         for (String path : more) {
-            if (path.length() > 0) {
+            if (!path.isEmpty()) {
                 if (sb.length() > 0) {
                     sb.append('/');
                 }

src/java.base/share/classes/jdk/internal/jrtfs/JrtPath.java

@@ -88,7 +88,7 @@ final class JrtPath implements Path {
 
     @Override
     public final JrtPath getFileName() {
-        if (path.length() == 0)
+        if (path.isEmpty())
             return this;
         if (path.length() == 1 && path.charAt(0) == '/')
             return null;
@@ -210,7 +210,7 @@ final class JrtPath implements Path {
         if (o.equals(this)) {
             return new JrtPath(jrtfs, "", true);
         }
-        if (path.length() == 0) {
+        if (path.isEmpty()) {
             return o;
         }
         if (jrtfs != o.jrtfs || isAbsolute() != o.isAbsolute()) {
@@ -262,16 +262,16 @@ final class JrtPath implements Path {
 
     @Override
     public final boolean isAbsolute() {
-        return path.length() > 0 && path.charAt(0) == '/';
+        return !path.isEmpty() && path.charAt(0) == '/';
     }
 
     @Override
     public final JrtPath resolve(Path other) {
         final JrtPath o = checkPath(other);
-        if (this.path.length() == 0 || o.isAbsolute()) {
+        if (this.path.isEmpty() || o.isAbsolute()) {
             return o;
         }
-        if (o.path.length() == 0) {
+        if (o.path.isEmpty()) {
             return this;
         }
         StringBuilder sb = new StringBuilder(path.length() + o.path.length() + 1);
@@ -301,7 +301,7 @@ final class JrtPath implements Path {
         }
         int off = op.length();
         if (off == 0) {
-            return tp.length() == 0;
+            return tp.isEmpty();
         }
         // check match is on name boundary
         return tp.length() == off || tp.charAt(off) == '/' ||

src/java.base/share/classes/jdk/internal/loader/ClassLoaders.java

@@ -59,7 +59,7 @@ public class ClassLoaders {
         // -Xbootclasspath/a or -javaagent with Boot-Class-Path attribute
         String append = VM.getSavedProperty("jdk.boot.class.path.append");
         BOOT_LOADER =
-            new BootClassLoader((append != null && append.length() > 0)
+            new BootClassLoader((append != null && !append.isEmpty())
                 ? new URLClassPath(append, true)
                 : null);
         PLATFORM_LOADER = new PlatformClassLoader(BOOT_LOADER);
@@ -70,7 +70,7 @@ public class ClassLoaders {
         // contrary, we drop this historic interpretation of the empty
         // string and instead treat it as unspecified.
         String cp = System.getProperty("java.class.path");
-        if (cp == null || cp.length() == 0) {
+        if (cp == null || cp.isEmpty()) {
             String initialModuleName = System.getProperty("jdk.module.main");
             cp = (initialModuleName == null) ? "" : null;
         }

src/java.base/share/classes/jdk/internal/loader/URLClassPath.java

@@ -190,7 +190,7 @@ public class URLClassPath {
                 String element = (next == -1)
                     ? cp.substring(off)
                     : cp.substring(off, next);
-                if (element.length() > 0 || !skipEmptyElements) {
+                if (!element.isEmpty() || !skipEmptyElements) {
                     URL url = toFileURL(element);
                     if (url != null) path.add(url);
                 }

src/java.base/share/classes/jdk/internal/module/Checks.java

@@ -62,22 +62,6 @@ public final class Checks {
         return name;
     }
 
-    /**
-     * Returns {@code true} if the given name is a legal module name.
-     */
-    public static boolean isModuleName(String name) {
-        int next;
-        int off = 0;
-        while ((next = name.indexOf('.', off)) != -1) {
-            String id = name.substring(off, next);
-            if (!isJavaIdentifier(id))
-                return false;
-            off = next+1;
-        }
-        String last = name.substring(off);
-        return isJavaIdentifier(last);
-    }
-
     /**
      * Checks a name to ensure that it's a legal package name.
      *
@@ -181,20 +165,20 @@ public final class Checks {
     }
 
     /**
-     * Returns true if the given char sequence is a legal Java identifier,
+     * Returns true if the given string is a legal Java identifier,
      * otherwise false.
      */
-    private static boolean isJavaIdentifier(CharSequence cs) {
+    private static boolean isJavaIdentifier(String str) {
-        if (cs.length() == 0 || RESERVED.contains(cs))
+        if (str.isEmpty() || RESERVED.contains(str))
             return false;
 
-        int first = Character.codePointAt(cs, 0);
+        int first = Character.codePointAt(str, 0);
         if (!Character.isJavaIdentifierStart(first))
             return false;
 
         int i = Character.charCount(first);
-        while (i < cs.length()) {
+        while (i < str.length()) {
-            int cp = Character.codePointAt(cs, i);
+            int cp = Character.codePointAt(str, i);
             if (!Character.isJavaIdentifierPart(cp))
                 return false;
             i += Character.charCount(cp);

src/java.base/share/classes/jdk/internal/module/ModuleBootstrap.java

@@ -604,7 +604,8 @@ public final class ModuleBootstrap {
             Set<String> modules = new HashSet<>();
             while (value != null) {
                 for (String s : value.split(",")) {
-                    if (s.length() > 0) modules.add(s);
+                    if (!s.isEmpty())
+                        modules.add(s);
                 }
                 index++;
                 value = getAndRemoveProperty(prefix + index);
@@ -895,7 +896,7 @@ public final class ModuleBootstrap {
             List<String> values = map.computeIfAbsent(key, k -> new ArrayList<>());
             int ntargets = 0;
             for (String s : rhs.split(regex)) {
-                if (s.length() > 0) {
+                if (!s.isEmpty()) {
                     values.add(s);
                     ntargets++;
                 }

src/java.base/share/classes/jdk/internal/module/ModulePatcher.java

@@ -552,7 +552,7 @@ public final class ModulePatcher {
         public Stream<String> list() throws IOException {
             return Files.walk(dir, Integer.MAX_VALUE)
                         .map(f -> Resources.toResourceName(dir, f))
-                        .filter(s -> s.length() > 0);
+                        .filter(s -> !s.isEmpty());
         }
     }
 

src/java.base/share/classes/jdk/internal/module/ModulePath.java

@@ -546,7 +546,7 @@ public class ModulePath implements ModuleFinder {
                     = new BufferedReader(new InputStreamReader(in, "UTF-8"));
                 String cn;
                 while ((cn = nextLine(reader)) != null) {
-                    if (cn.length() > 0) {
+                    if (!cn.isEmpty()) {
                         String pn = packageName(cn);
                         if (!packages.contains(pn)) {
                             String msg = "Provider class " + cn + " not in module";
@@ -599,7 +599,7 @@ public class ModulePath implements ModuleFinder {
         mn = Patterns.REPEATING_DOTS.matcher(mn).replaceAll(".");
 
         // drop leading dots
-        if (mn.length() > 0 && mn.charAt(0) == '.')
+        if (!mn.isEmpty() && mn.charAt(0) == '.')
             mn = Patterns.LEADING_DOTS.matcher(mn).replaceAll("");
 
         // drop trailing dots

src/java.base/share/classes/jdk/internal/module/Resources.java

@@ -78,7 +78,7 @@ public final class Resources {
         String s = dir.relativize(file)
                       .toString()
                       .replace(File.separatorChar, '/');
-        if (s.length() > 0 && Files.isDirectory(file))
+        if (!s.isEmpty() && Files.isDirectory(file))
             s += "/";
         return s;
     }

src/java.base/share/classes/jdk/internal/module/SystemModuleFinders.java

@@ -83,7 +83,7 @@ public final class SystemModuleFinders {
         if (value == null) {
             USE_FAST_PATH = true;
         } else {
-            USE_FAST_PATH = (value.length() > 0) && !Boolean.parseBoolean(value);
+            USE_FAST_PATH = !value.isEmpty() && !Boolean.parseBoolean(value);
         }
     }
 

src/java.base/share/classes/jdk/internal/org/objectweb/asm/TypePath.java

@@ -147,7 +147,7 @@ public final class TypePath {
       * @return the corresponding TypePath object, or {@literal null} if the path is empty.
       */
     public static TypePath fromString(final String typePath) {
-        if (typePath == null || typePath.length() == 0) {
+        if (typePath == null || typePath.isEmpty()) {
             return null;
         }
         int typePathLength = typePath.length();

src/java.base/share/classes/jdk/internal/org/objectweb/asm/util/CheckMethodAdapter.java

@@ -1314,7 +1314,7 @@ public class CheckMethodAdapter extends MethodVisitor {
       * @param message the message to use in case of error.
       */
     static void checkMethodIdentifier(final int version, final String name, final String message) {
-        if (name == null || name.length() == 0) {
+        if (name == null || name.isEmpty()) {
             throw new IllegalArgumentException(INVALID + message + MUST_NOT_BE_NULL_OR_EMPTY);
         }
         if ((version & 0xFFFF) >= Opcodes.V1_5) {
@@ -1347,7 +1347,7 @@ public class CheckMethodAdapter extends MethodVisitor {
       * @param message the message to use in case of error.
       */
     static void checkInternalName(final int version, final String name, final String message) {
-        if (name == null || name.length() == 0) {
+        if (name == null || name.isEmpty()) {
             throw new IllegalArgumentException(INVALID + message + MUST_NOT_BE_NULL_OR_EMPTY);
         }
         if (name.charAt(0) == '[') {
@@ -1457,7 +1457,7 @@ public class CheckMethodAdapter extends MethodVisitor {
       * @param descriptor the string to be checked.
       */
     static void checkMethodDescriptor(final int version, final String descriptor) {
-        if (descriptor == null || descriptor.length() == 0) {
+        if (descriptor == null || descriptor.isEmpty()) {
             throw new IllegalArgumentException("Invalid method descriptor (must not be null or empty)");
         }
         if (descriptor.charAt(0) != '(' || descriptor.length() < 3) {

src/java.base/share/classes/jdk/internal/org/objectweb/asm/util/CheckSignatureAdapter.java

@@ -365,7 +365,7 @@ public class CheckSignatureAdapter extends SignatureVisitor {
     }
 
     private void checkClassName(final String name, final String message) {
-        if (name == null || name.length() == 0) {
+        if (name == null || name.isEmpty()) {
             throw new IllegalArgumentException(INVALID + message + " (must not be null or empty)");
         }
         for (int i = 0; i < name.length(); ++i) {
@@ -377,7 +377,7 @@ public class CheckSignatureAdapter extends SignatureVisitor {
     }
 
     private void checkIdentifier(final String name, final String message) {
-        if (name == null || name.length() == 0) {
+        if (name == null || name.isEmpty()) {
             throw new IllegalArgumentException(INVALID + message + " (must not be null or empty)");
         }
         for (int i = 0; i < name.length(); ++i) {

src/java.base/share/classes/jdk/internal/reflect/UnsafeFieldAccessorImpl.java

@@ -151,10 +151,10 @@ abstract class UnsafeFieldAccessorImpl extends FieldAccessorImpl {
         if (isFinal)
             err += " final";
         err += " " + field.getType().getName() + " field " + getQualifiedFieldName() + " to ";
-        if (attemptedValue.length() > 0) {
+        if (!attemptedValue.isEmpty()) {
             err += "(" + attemptedType + ")" + attemptedValue;
         } else {
-            if (attemptedType.length() > 0)
+            if (!attemptedType.isEmpty())
                 err += attemptedType;
             else
                 err += "null value";

src/java.base/share/classes/jdk/internal/util/jar/JarIndex.java

@@ -291,7 +291,7 @@ public class JarIndex {
         while((line = br.readLine()) != null && !line.endsWith(".jar"));
 
         for(;line != null; line = br.readLine()) {
-            if (line.length() == 0)
+            if (line.isEmpty())
                 continue;
 
             if (line.endsWith(".jar")) {

src/java.base/share/classes/jdk/internal/util/xml/PropertiesDefaultHandler.java

@@ -103,7 +103,7 @@ public class PropertiesDefaultHandler extends DefaultHandler {
             writer.writeStartDocument();
             writer.writeDTD(PROPS_DTD_DECL);
             writer.writeStartElement(ELEMENT_ROOT);
-            if (comment != null && comment.length() > 0) {
+            if (comment != null && !comment.isEmpty()) {
                 writer.writeStartElement(ELEMENT_COMMENT);
                 writer.writeCharacters(comment);
                 writer.writeEndElement();

src/java.base/share/classes/jdk/internal/util/xml/impl/Parser.java

@@ -1591,7 +1591,7 @@ public abstract class Parser {
                             str = name(false);
                             //          PI target name may not be empty string [#2.6]
                             //          PI target name 'XML' is reserved [#2.6]
-                            if ((str.length() == 0)
+                            if ((str.isEmpty())
                                     || (mXml.name.equals(str.toLowerCase()) == true)) {
                                 panic(FAULT);
                             }

src/java.base/share/classes/jdk/internal/util/xml/impl/XMLStreamWriterImpl.java

@@ -205,7 +205,7 @@ public class XMLStreamWriterImpl implements XMLStreamWriter {
      * @throws XMLStreamException
      */
     public void writeStartElement(String localName) throws XMLStreamException {
-        if (localName == null || localName.length() == 0) {
+        if (localName == null || localName.isEmpty()) {
             throw new XMLStreamException("Local Name cannot be null or empty");
         }
 
@@ -420,7 +420,7 @@ public class XMLStreamWriterImpl implements XMLStreamWriter {
     }
 
     private void writeXMLContent(String content) throws XMLStreamException {
-        if ((content != null) && (content.length() > 0)) {
+        if (content != null && !content.isEmpty()) {
             writeXMLContent(content,
                     _escapeCharacters, // boolean = escapeChars
                     false);             // false = escapeDoubleQuotes

src/java.base/share/classes/sun/invoke/util/BytecodeName.java

@@ -451,7 +451,7 @@ public class BytecodeName {
      * @return true if the name is non-empty and all of its characters are safe
      */
     public static boolean isSafeBytecodeName(String s) {
-        if (s.length() == 0)  return false;
+        if (s.isEmpty())  return false;
         // check occurrences of each DANGEROUS char
         for (char xc : DANGEROUS_CHARS_A) {
             if (xc == ESCAPE_C)  continue;  // not really that dangerous
@@ -476,7 +476,7 @@ public class BytecodeName {
     }
 
     private static String mangle(String s) {
-        if (s.length() == 0)
+        if (s.isEmpty())
             return NULL_ESCAPE;
 
         // build this lazily, when we first need an escape:

src/java.base/share/classes/sun/net/TransferProtocolClient.java

@@ -76,7 +76,7 @@ public class TransferProtocolClient extends NetworkClient {
                 System.out.print(response);
             }
 
-            if (response.length() == 0) {
+            if (response.isEmpty()) {
                 code = -1;
             } else {
                 try {

src/java.base/share/classes/sun/net/ftp/impl/FtpClient.java

@@ -433,7 +433,7 @@ public class FtpClient extends sun.net.ftp.FtpClient {
                 logger.finest("Server [" + serverAddr + "] --> " + response);
             }
 
-            if (response.length() == 0) {
+            if (response.isEmpty()) {
                 code = -1;
             } else {
                 try {
@@ -1049,7 +1049,7 @@ public class FtpClient extends sun.net.ftp.FtpClient {
         if (!isConnected()) {
             throw new sun.net.ftp.FtpProtocolException("Not connected yet", FtpReplyCode.BAD_SEQUENCE);
         }
-        if (user == null || user.length() == 0) {
+        if (user == null || user.isEmpty()) {
             throw new IllegalArgumentException("User name can't be null or empty");
         }
         tryLogin(user, password);
@@ -1088,7 +1088,7 @@ public class FtpClient extends sun.net.ftp.FtpClient {
         if (!isConnected()) {
             throw new sun.net.ftp.FtpProtocolException("Not connected yet", FtpReplyCode.BAD_SEQUENCE);
         }
-        if (user == null || user.length() == 0) {
+        if (user == null || user.isEmpty()) {
             throw new IllegalArgumentException("User name can't be null or empty");
         }
         tryLogin(user, password);
@@ -1152,7 +1152,7 @@ public class FtpClient extends sun.net.ftp.FtpClient {
      * @exception <code>FtpProtocolException</code>
      */
     public sun.net.ftp.FtpClient changeDirectory(String remoteDirectory) throws sun.net.ftp.FtpProtocolException, IOException {
-        if (remoteDirectory == null || "".equals(remoteDirectory)) {
+        if (remoteDirectory == null || remoteDirectory.isEmpty()) {
             throw new IllegalArgumentException("directory can't be null or empty");
         }
 
@@ -1738,7 +1738,7 @@ public class FtpClient extends sun.net.ftp.FtpClient {
      * @throws IOException if an error occurs during the transmission.
      */
     public long getSize(String path) throws sun.net.ftp.FtpProtocolException, IOException {
-        if (path == null || path.length() == 0) {
+        if (path == null || path.isEmpty()) {
             throw new IllegalArgumentException("path can't be null or empty");
         }
         issueCommandCheck("SIZE " + path);

src/java.base/share/classes/sun/net/spi/DefaultProxySelector.java

@@ -238,7 +238,7 @@ public class DefaultProxySelector extends ProxySelector {
                                 if (phost != null && phost.length() != 0)
                                     break;
                             }
-                            if (phost == null || phost.length() == 0) {
+                            if (phost == null || phost.isEmpty()) {
                                 /**
                                  * No system property defined for that
                                  * protocol. Let's check System Proxy
@@ -267,7 +267,7 @@ public class DefaultProxySelector extends ProxySelector {
                                             nprop.hostsSource = null;
                                             nprop.pattern = null;
                                         }
-                                    } else if (nphosts.length() != 0) {
+                                    } else if (!nphosts.isEmpty()) {
                                         // add the required default patterns
                                         // but only if property no set. If it
                                         // is empty, leave empty.

src/java.base/share/classes/sun/net/www/HeaderParser.java

@@ -226,7 +226,7 @@ public class HeaderParser {
         for (int i=0; k.hasNext(); i++) {
             String key = k.next();
             String val = findValue (i);
-            if (val != null && "".equals (val)) {
+            if (val != null && val.isEmpty()) {
                 val = null;
             }
             sb.append(" {").append(key).append(val == null ? "" : "," + val)

src/java.base/share/classes/sun/net/www/MimeEntry.java

@@ -201,9 +201,7 @@ public class MimeEntry implements Cloneable {
     }
 
     private boolean isStarred(String typeName) {
-        return (typeName != null)
+        return typeName != null && typeName.endsWith("/*");
-            && (typeName.length() > 0)
-            && (typeName.endsWith("/*"));
     }
 
     /**
@@ -300,7 +298,7 @@ public class MimeEntry implements Cloneable {
         }
 
         String extensions = getExtensionsAsList();
-        if (extensions.length() > 0) {
+        if (!extensions.isEmpty()) {
             sj.add("file_extensions=" + extensions);
         }
 

src/java.base/share/classes/sun/net/www/MimeLauncher.java

@@ -162,7 +162,7 @@ class MimeLauncher extends Thread {
        location the application.  If a valid path is not found, it
        returns false else true.  */
     private boolean findExecutablePath(String str) {
-        if (str == null || str.length() == 0) {
+        if (str == null || str.isEmpty()) {
             return false;
         }
 

src/java.base/share/classes/sun/net/www/ParseUtil.java

@@ -536,8 +536,7 @@ public final class ParseUtil {
         throws URISyntaxException
     {
         if (scheme != null) {
-            if ((path != null)
+            if (path != null && !path.isEmpty() && path.charAt(0) != '/')
-                && ((path.length() > 0) && (path.charAt(0) != '/')))
                 throw new URISyntaxException(s,
                                              "Relative path in absolute URI");
         }

src/java.base/share/classes/sun/net/www/http/HttpClient.java

@@ -603,7 +603,7 @@ public class HttpClient extends NetworkClient {
             StringBuilder result = new StringBuilder(128);
             result.append(url.getProtocol());
             result.append(":");
-            if (url.getAuthority() != null && url.getAuthority().length() > 0) {
+            if (url.getAuthority() != null && !url.getAuthority().isEmpty()) {
                 result.append("//");
                 result.append(url.getAuthority());
             }
@@ -619,7 +619,7 @@ public class HttpClient extends NetworkClient {
         } else {
             fileName = url.getFile();
 
-            if ((fileName == null) || (fileName.length() == 0)) {
+            if ((fileName == null) || (fileName.isEmpty())) {
                 fileName = "/";
             } else if (fileName.charAt(0) == '?') {
                 /* HTTP/1.1 spec says in 5.1.2. about Request-URI:

src/java.base/share/classes/sun/net/www/protocol/ftp/FtpURLConnection.java

@@ -341,7 +341,7 @@ public class FtpURLConnection extends URLConnection {
                 path.charAt(0) == '/') {
             path = path.substring(1);
         }
-        if (path == null || path.length() == 0) {
+        if (path == null || path.isEmpty()) {
             path = "./";
         }
         if (!path.endsWith("/")) {
@@ -555,7 +555,7 @@ public class FtpURLConnection extends URLConnection {
         }
 
         decodePath(url.getPath());
-        if (filename == null || filename.length() == 0) {
+        if (filename == null || filename.isEmpty()) {
             throw new IOException("illegal filename for a PUT");
         }
         try {

src/java.base/share/classes/sun/net/www/protocol/http/AuthenticationInfo.java

@@ -248,7 +248,7 @@ public abstract class AuthenticationInfo extends AuthCacheValue implements Clone
         this.realm = realm;
 
         String urlPath = url.getPath();
-        if (urlPath.length() == 0)
+        if (urlPath.isEmpty())
             this.path = urlPath;
         else {
             this.path = reducePath (urlPath);

src/java.base/share/classes/sun/net/www/protocol/http/DigestAuthentication.java

@@ -279,7 +279,7 @@ class DigestAuthentication extends AuthenticationInfo {
         if (s == null || !s.equals("true"))
             return false;
         String newNonce = p.findValue ("nonce");
-        if (newNonce == null || "".equals(newNonce)) {
+        if (newNonce == null || newNonce.isEmpty()) {
             return false;
         }
         params.setNonce (newNonce);
@@ -323,7 +323,7 @@ class DigestAuthentication extends AuthenticationInfo {
                         + authMethod.substring(1).toLowerCase();
         }
         String algorithm = p.findValue("algorithm");
-        if (algorithm == null || "".equals(algorithm)) {
+        if (algorithm == null || algorithm.isEmpty()) {
             algorithm = "MD5";  // The default, accoriding to rfc2069
         }
         params.setAlgorithm (algorithm);
@@ -451,7 +451,7 @@ class DigestAuthentication extends AuthenticationInfo {
             }
             /* Check if there is a nextnonce field */
             String nextnonce = p.findValue ("nextnonce");
-            if (nextnonce != null && ! "".equals(nextnonce)) {
+            if (nextnonce != null && !nextnonce.isEmpty()) {
                 params.setNonce (nextnonce);
             }
 

src/java.base/share/classes/sun/net/www/protocol/http/HttpURLConnection.java

@@ -3026,7 +3026,7 @@ public class HttpURLConnection extends java.net.HttpURLConnection {
 
             // Filtering only if there is a cookie handler. [Assumption: the
             // cookie handler will store/retrieve the HttpOnly cookies]
-            if (cookieHandler == null || value.length() == 0)
+            if (cookieHandler == null || value.isEmpty())
                 return value;
 
             JavaNetHttpCookieAccess access =