8221307: String.substring() OOB exception on start index reports improper information

Reviewed-by: rriggs, redestad

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

@@ -1868,18 +1868,7 @@ public final class String
      *             length of this {@code String} object.
      */
     public String substring(int beginIndex) {
-        if (beginIndex < 0) {
+        return substring(beginIndex, length());
-            throw new StringIndexOutOfBoundsException(beginIndex);
-        }
-        int subLen = length() - beginIndex;
-        if (subLen < 0) {
-            throw new StringIndexOutOfBoundsException(subLen);
-        }
-        if (beginIndex == 0) {
-            return this;
-        }
-        return isLatin1() ? StringLatin1.newString(value, beginIndex, subLen)
-                          : StringUTF16.newString(value, beginIndex, subLen);
     }
 
     /**
@@ -3677,7 +3666,7 @@ public final class String
     static void checkIndex(int index, int length) {
         if (index < 0 || index >= length) {
             throw new StringIndexOutOfBoundsException("index " + index +
-                                                      ",length " + length);
+                                                      ", length " + length);
         }
     }
 
@@ -3688,7 +3677,7 @@ public final class String
     static void checkOffset(int offset, int length) {
         if (offset < 0 || offset > length) {
             throw new StringIndexOutOfBoundsException("offset " + offset +
-                                                      ",length " + length);
+                                                      ", length " + length);
         }
     }
 

src/java.base/share/classes/java/lang/StringUTF16.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2019, 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
@@ -489,7 +489,7 @@ final class StringUTF16 {
             final char lo = Character.lowSurrogate(ch);
             checkBoundsBeginEnd(fromIndex, max, value);
             for (int i = fromIndex; i < max - 1; i++) {
-                if (getChar(value, i) == hi && getChar(value, i + 1 ) == lo) {
+                if (getChar(value, i) == hi && getChar(value, i + 1) == lo) {
                     return i;
                 }
             }

test/micro/org/openjdk/bench/java/lang/StringSubstring.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2019, 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.
+ */
+
+package org.openjdk.bench.java.lang;
+
+import org.openjdk.jmh.annotations.*;
+import java.util.concurrent.TimeUnit;
+
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@State(Scope.Benchmark)
+public class StringSubstring {
+
+    public String s = new String("An arbitrary string that happened to be of length 52");
+
+    @Benchmark
+    public String from26toEnd0() {
+        return s.substring(26);
+    }
+
+    @Benchmark
+    public String from26toEnd1() {
+        return s.substring(26, s.length());
+    }
+}