6952330: Fix for 6933217 broke contract of StringBuffer.ensureCapacity

Summary: make sure to grow with size => size * 2 + 2
Reviewed-by: dholmes, chegar, ohair

src/share/classes/java/lang/AbstractStringBuilder.java

@@ -117,7 +117,7 @@ abstract class AbstractStringBuilder implements Appendable, CharSequence {
      * size check or synchronization.
      */
     void expandCapacity(int minimumCapacity) {
-        int newCapacity = value.length * 2;
+        int newCapacity = value.length * 2 + 2;
         if (newCapacity - minimumCapacity < 0)
             newCapacity = minimumCapacity;
         if (newCapacity < 0) {

test/java/lang/StringBuffer/Capacity.java

+/*
+ * Copyright 2010 Google Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * @test
+ * @bug 6952330
+ * @summary Test StringBuffer/StringBuilder capacity handling.
+ */
+
+import java.util.Random;
+
+public class Capacity {
+    void test(String[] args) throws Throwable {
+        Random rnd = new Random();
+        int[] sizes = { 0, 1, rnd.nextInt(10), rnd.nextInt(1000) };
+        for (int size : sizes) {
+            equal(16, new StringBuffer().capacity());
+            equal(16, new StringBuilder().capacity());
+            StringBuffer buff = new StringBuffer(size);
+            StringBuilder bild = new StringBuilder(size);
+            equal(size, buff.capacity());
+            equal(size, bild.capacity());
+            buff.ensureCapacity(size);
+            bild.ensureCapacity(size);
+            equal(size, buff.capacity());
+            equal(size, bild.capacity());
+            buff.ensureCapacity(size+1);
+            bild.ensureCapacity(size+1);
+            equal(size*2+2, buff.capacity());
+            equal(size*2+2, bild.capacity());
+            size = buff.capacity();
+            buff.ensureCapacity(size*2+1);
+            bild.ensureCapacity(size*2+1);
+            equal(size*2+2, buff.capacity());
+            equal(size*2+2, bild.capacity());
+            size = buff.capacity();
+            int newSize = size * 2 + 3;
+            buff.ensureCapacity(newSize);
+            bild.ensureCapacity(newSize);
+            equal(newSize, buff.capacity());
+            equal(newSize, bild.capacity());
+            buff.ensureCapacity(0);
+            bild.ensureCapacity(0);
+            equal(newSize, buff.capacity());
+            equal(newSize, bild.capacity());
+        }
+    }
+
+    //--------------------- Infrastructure ---------------------------
+    volatile int passed = 0, failed = 0;
+    void pass() {passed++;}
+    void fail() {failed++; Thread.dumpStack();}
+    void fail(String msg) {System.err.println(msg); fail();}
+    void unexpected(Throwable t) {failed++; t.printStackTrace();}
+    void check(boolean cond) {if (cond) pass(); else fail();}
+    void equal(Object x, Object y) {
+        if (x == null ? y == null : x.equals(y)) pass();
+        else fail(x + " not equal to " + y);}
+    public static void main(String[] args) throws Throwable {
+        new Capacity().instanceMain(args);}
+    public void instanceMain(String[] args) throws Throwable {
+        try {test(args);} catch (Throwable t) {unexpected(t);}
+        System.out.printf("%nPassed = %d, failed = %d%n%n", passed, failed);
+        if (failed > 0) throw new AssertionError("Some tests failed");}
+}