8013528: Provide SharedSecrets access to String(char[], boolean) constructor

Reviewed-by: martin, alanb, chegar, plevart

src/share/classes/java/lang/System.java

@@ -1246,6 +1246,9 @@ public final class System {
             public StackTraceElement getStackTraceElement(Throwable t, int i) {
                 return t.getStackTraceElement(i);
             }
+            public String newStringUnsafe(char[] chars) {
+                return new String(chars, true);
+            }
         });
     }
 }

src/share/classes/sun/misc/JavaLangAccess.java

@@ -97,4 +97,14 @@ public interface JavaLangAccess {
      * Returns the ith StackTraceElement for the given throwable.
      */
     StackTraceElement getStackTraceElement(Throwable t, int i);
+
+    /**
+     * Returns a new string backed by the provided character array. The
+     * character array is not copied and must never be modified after the
+     * String is created, in order to fulfill String's contract.
+     *
+     * @param chars the character array to back the string
+     * @return a newly created string whose content is the character array
+     */
+    String newStringUnsafe(char[] chars);
 }

test/sun/misc/JavaLangAccess/NewUnsafeString.java

+/*
+ * Copyright (c) 2012, 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.
+ */
+
+import java.util.Objects;
+import java.util.Comparators;
+import sun.misc.JavaLangAccess;
+import sun.misc.SharedSecrets;
+
+/*
+ * @test
+ * @summary Test JavaLangAccess.newUnsafeString
+ * @bug 8013528
+ * @compile -XDignore.symbol.file NewUnsafeString.java
+ */
+public class NewUnsafeString {
+
+    static final JavaLangAccess jla = SharedSecrets.getJavaLangAccess();
+
+    public static void testNewUnsafeString() {
+        String benchmark = "exemplar";
+        String constructorCopy = new String(benchmark);
+        char[] jlaChars = benchmark.toCharArray();
+        String jlaCopy = jla.newStringUnsafe(jlaChars);
+
+        if (benchmark == constructorCopy) {
+            throw new Error("should be different instances");
+        }
+        if (!benchmark.equals(constructorCopy)) {
+            throw new Error("Copy not equal");
+        }
+        if (0 != Objects.compare(benchmark, constructorCopy, Comparators.naturalOrder())) {
+            throw new Error("Copy not equal");
+        }
+
+        if (benchmark == jlaCopy) {
+            throw new Error("should be different instances");
+        }
+        if (!benchmark.equals(jlaCopy)) {
+            throw new Error("Copy not equal");
+        }
+        if (0 != Objects.compare(benchmark, jlaCopy, Comparators.naturalOrder())) {
+            throw new Error("Copy not equal");
+        }
+
+        if (constructorCopy == jlaCopy) {
+            throw new Error("should be different instances");
+        }
+        if (!constructorCopy.equals(jlaCopy)) {
+            throw new Error("Copy not equal");
+        }
+        if (0 != Objects.compare(constructorCopy, jlaCopy, Comparators.naturalOrder())) {
+            throw new Error("Copy not equal");
+        }
+
+        // The following is extremely "evil". Never ever do this in non-test code.
+        jlaChars[0] = 'X';
+        if (!"Xxemplar".equals(jlaCopy)) {
+            throw new Error("jla.newStringUnsafe did not use provided string");
+        }
+
+    }
+
+    public static void main(String[] args) {
+        testNewUnsafeString();
+    }
+}