8197594: String#repeat

Reviewed-by: smarks, psandoz, plevart, rriggs, redestad

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

@@ -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);
+    }
+
     ////////////////////////////////////////////////////////////////
 
     /**

test/jdk/java/lang/String/StringRepeat.java

@@ -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();
+            }
+        }
+    }
+}