diff --git a/src/java.base/share/classes/java/io/ExpiringCache.java b/src/java.base/share/classes/java/io/ExpiringCache.java
index 92aeb6dbd8f..96959e00158 100644
--- a/src/java.base/share/classes/java/io/ExpiringCache.java
+++ b/src/java.base/share/classes/java/io/ExpiringCache.java
@@ -23,25 +23,23 @@
  * questions.
  */
 
-/*
- */
-
 package java.io;
 
 import java.util.Map;
 import java.util.LinkedHashMap;
 import java.util.Set;
 
-class ExpiringCache {
+final class ExpiringCache {
 
     private static final int QUERY_OVERFLOW = 300;
     private static final int MAX_ENTRIES = 200;
     private final long millisUntilExpiration;
     private final Map<String,Entry> map;
+
     // Clear out old entries every few queries
     private int queryCount;
 
-    static class Entry {
+    static final class Entry {
         private long timestamp;
         private String val;
 
diff --git a/src/java.base/share/classes/java/io/ObjectInputStream.java b/src/java.base/share/classes/java/io/ObjectInputStream.java
index 08e895530dc..7c02fba8103 100644
--- a/src/java.base/share/classes/java/io/ObjectInputStream.java
+++ b/src/java.base/share/classes/java/io/ObjectInputStream.java
@@ -3862,7 +3862,7 @@ public class ObjectInputStream
      * as memory conservation, it does not enforce this constraint.
      */
     // REMIND: add full description of exception propagation algorithm?
-    private static class HandleTable {
+    private static final class HandleTable {
 
         /* status codes indicating whether object has associated exception */
         private static final byte STATUS_OK = 1;
diff --git a/src/java.base/share/classes/java/io/ObjectOutputStream.java b/src/java.base/share/classes/java/io/ObjectOutputStream.java
index b6d3b1e5915..d3f3e05a4ac 100644
--- a/src/java.base/share/classes/java/io/ObjectOutputStream.java
+++ b/src/java.base/share/classes/java/io/ObjectOutputStream.java
@@ -1754,7 +1754,7 @@ public class ObjectOutputStream
      * bracketed by block data markers (see object serialization specification
      * for details).
      */
-    private static class BlockDataOutputStream
+    private static final class BlockDataOutputStream
         extends OutputStream implements DataOutput
     {
         /** maximum data block length */
@@ -2260,7 +2260,7 @@ public class ObjectOutputStream
      * Lightweight identity hash table which maps objects to integer handles,
      * assigned in ascending order.
      */
-    private static class HandleTable {
+    private static final class HandleTable {
 
         /* number of mappings in table/next available handle */
         private int size;
@@ -2385,7 +2385,7 @@ public class ObjectOutputStream
      * Lightweight identity hash table which maps objects to replacement
      * objects.
      */
-    private static class ReplaceTable {
+    private static final class ReplaceTable {
 
         /* maps object -> index */
         private final HandleTable htab;
@@ -2449,7 +2449,7 @@ public class ObjectOutputStream
      * Stack to keep debug information about the state of the
      * serialization process, for embedding in exception messages.
      */
-    private static class DebugTraceInfoStack {
+    private static final class DebugTraceInfoStack {
         private final List<String> stack;
 
         DebugTraceInfoStack() {
diff --git a/src/java.base/share/classes/java/io/ObjectStreamClass.java b/src/java.base/share/classes/java/io/ObjectStreamClass.java
index bab66fd4809..c01430912eb 100644
--- a/src/java.base/share/classes/java/io/ObjectStreamClass.java
+++ b/src/java.base/share/classes/java/io/ObjectStreamClass.java
@@ -1871,7 +1871,7 @@ public final class ObjectStreamClass implements Serializable {
      * Class for computing and caching field/constructor/method signatures
      * during serialVersionUID calculation.
      */
-    private static class MemberSignature {
+    private static final class MemberSignature {
 
         public final Member member;
         public final String name;
@@ -1902,7 +1902,7 @@ public final class ObjectStreamClass implements Serializable {
      * Class for setting and retrieving serializable field values in batch.
      */
     // REMIND: dynamically generate these?
-    private static class FieldReflector {
+    private static final class FieldReflector {
 
         /** handle for performing unsafe operations */
         private static final Unsafe UNSAFE = Unsafe.getUnsafe();
diff --git a/src/java.base/share/classes/java/io/ProxyingConsole.java b/src/java.base/share/classes/java/io/ProxyingConsole.java
index 4be206a1590..71068530300 100644
--- a/src/java.base/share/classes/java/io/ProxyingConsole.java
+++ b/src/java.base/share/classes/java/io/ProxyingConsole.java
@@ -145,7 +145,7 @@ final class ProxyingConsole extends Console {
         return delegate.charset();
     }
 
-    private static class WrappingReader extends Reader {
+    private static final class WrappingReader extends Reader {
         private final Reader r;
         private final Object lock;
 
@@ -168,7 +168,7 @@ final class ProxyingConsole extends Console {
         }
     }
 
-    private static class WrappingWriter extends PrintWriter {
+    private static final class WrappingWriter extends PrintWriter {
         private final PrintWriter pw;
         private final Object lock;