8197594: String#repeat

Reviewed-by: smarks, psandoz, plevart, rriggs, redestad
This commit is contained in:
Jim Laskey 2018-03-01 15:45:51 -04:00
parent 95b1eef0da
commit b4d4d8f66c
2 changed files with 183 additions and 0 deletions
src/java.base/share/classes/java/lang
test/jdk/java/lang/String

@ -2963,6 +2963,56 @@ public final class String
*/
public native String intern();
/**
* Returns a string whose value is the concatenation of this
* string repeated {@code count} times.
* <p>
* If this string is empty or count is zero then the empty
* string is returned.
*
* @param count number of times to repeat
*
* @return A string composed of this string repeated
* {@code count} times or the empty string if this
* string is empty or count is zero
*
* @throws IllegalArgumentException if the {@code count} is
* negative.
*
* @since 11
*/
public String repeat(int count) {
if (count < 0) {
throw new IllegalArgumentException("count is negative: " + count);
}
if (count == 1) {
return this;
}
final int len = value.length;
if (len == 0 || count == 0) {
return "";
}
if (len == 1) {
final byte[] single = new byte[count];
Arrays.fill(single, value[0]);
return new String(single, coder);
}
if (Integer.MAX_VALUE / count < len) {
throw new OutOfMemoryError("Repeating " + len + " bytes String " + count +
" times will produce a String exceeding maximum size.");
}
final int limit = len * count;
final byte[] multiple = new byte[limit];
System.arraycopy(value, 0, multiple, 0, len);
int copied = len;
for (int next = copied << 1; next < limit && 0 < next; next = next << 1) {
System.arraycopy(multiple, 0, multiple, copied, copied);
copied = next;
}
System.arraycopy(multiple, 0, multiple, copied, limit - copied);
return new String(multiple, coder);
}
////////////////////////////////////////////////////////////////
/**

@ -0,0 +1,133 @@
/*
* Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
/*
* @test
* @summary This exercises String#repeat patterns and limits.
* @run main/othervm -Xmx4G StringRepeat
*/
import java.nio.CharBuffer;
public class StringRepeat {
public static void main(String... arg) {
test1();
test2();
}
/*
* Varitions of repeat count.
*/
static int[] REPEATS = {
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
32, 64, 128, 256, 512, 1024, 64 * 1024, 1024 * 1024,
16 * 1024 * 1024
};
/*
* Varitions of Strings.
*/
static String[] STRINGS = new String[] {
"", "\0", " ", "a", "$", "\u2022",
"ab", "abc", "abcd", "abcde",
"The quick brown fox jumps over the lazy dog."
};
/*
* Repeat String function tests.
*/
static void test1() {
for (int repeat : REPEATS) {
for (String string : STRINGS) {
long limit = (long)string.length() * (long)repeat;
if ((long)(Integer.MAX_VALUE >> 1) <= limit) {
break;
}
verify(string.repeat(repeat), string, repeat);
}
}
}
/*
* Repeat String exception tests.
*/
static void test2() {
try {
"abc".repeat(-1);
throw new RuntimeException("No exception for negative repeat count");
} catch (IllegalArgumentException ex) {
// Correct
}
try {
"abc".repeat(Integer.MAX_VALUE - 1);
throw new RuntimeException("No exception for large repeat count");
} catch (OutOfMemoryError ex) {
// Correct
}
}
static String truncate(String string) {
if (string.length() < 80) {
return string;
}
return string.substring(0, 80) + "...";
}
/*
* Verify string repeat patterns.
*/
static void verify(String result, String string, int repeat) {
if (string.isEmpty() || repeat == 0) {
if (!result.isEmpty()) {
System.err.format("\"%s\".repeat(%d)%n", truncate(string), repeat);
System.err.format("Result \"%s\"%n", truncate(result));
System.err.format("Result expected to be empty, found string of length %d%n", result.length());
throw new RuntimeException();
}
} else {
int expected = 0;
int count = 0;
for (int offset = result.indexOf(string, expected);
0 <= offset;
offset = result.indexOf(string, expected)) {
count++;
if (offset != expected) {
System.err.format("\"%s\".repeat(%d)%n", truncate(string), repeat);
System.err.format("Result \"%s\"%n", truncate(result));
System.err.format("Repeat expected at %d, found at = %d%n", expected, offset);
throw new RuntimeException();
}
expected += string.length();
}
if (count != repeat) {
System.err.format("\"%s\".repeat(%d)%n", truncate(string), repeat);
System.err.format("Result \"%s\"%n", truncate(result));
System.err.format("Repeat count expected to be %d, found %d%n", repeat, count);
throw new RuntimeException();
}
}
}
}