--- /dev/null	2015-12-31 16:52:30.889242021 +0300
+++ new/src/java.base/share/classes/java/lang/StringConcatHelper.java	2016-01-22 12:15:47.504100741 +0300
@@ -0,0 +1,345 @@
+/*
+ * Copyright (c) 2015, 2015, 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 java.lang;
+
+/**
+ * Helper for string concatenation. These methods are mostly looked up with private lookups
+ * from {@link java.lang.invoke.StringConcatFactory}, and used in {@link java.lang.invoke.MethodHandle}
+ * combinators there.
+ */
+final class StringConcatHelper {
+
+    private StringConcatHelper() {
+        // no instantiation
+    }
+
+    /**
+     * Check for overflow, throw the exception on overflow.
+     * @param len String length
+     * @return length
+     */
+    private static int checkOverflow(int len) {
+        if (len < 0) {
+            throw new OutOfMemoryError("Overflow: String length out of range");
+        }
+        return len;
+    }
+
+    /**
+     * Mix value length into current length
+     * @param current current length
+     * @param value   value to mix in
+     * @return new length
+     */
+    static int mixLen(int current, boolean value) {
+        return checkOverflow(current + (value ? 4 : 5));
+    }
+
+    /**
+     * Mix value length into current length
+     * @param current current length
+     * @param value   value to mix in
+     * @return new length
+     */
+    static int mixLen(int current, byte value) {
+        return mixLen(current, (int)value);
+    }
+
+    /**
+     * Mix value length into current length
+     * @param current current length
+     * @param value   value to mix in
+     * @return new length
+     */
+    static int mixLen(int current, char value) {
+        return checkOverflow(current + 1);
+    }
+
+    /**
+     * Mix value length into current length
+     * @param current current length
+     * @param value   value to mix in
+     * @return new length
+     */
+    static int mixLen(int current, short value) {
+        return mixLen(current, (int)value);
+    }
+
+    /**
+     * Mix value length into current length
+     * @param current current length
+     * @param value   value to mix in
+     * @return new length
+     */
+    static int mixLen(int current, int value) {
+        return checkOverflow(current + Integer.stringSize(value));
+    }
+
+    /**
+     * Mix value length into current length
+     * @param current current length
+     * @param value   value to mix in
+     * @return new length
+     */
+    static int mixLen(int current, long value) {
+        return checkOverflow(current + Long.stringSize(value));
+    }
+
+    /**
+     * Mix value length into current length
+     * @param current current length
+     * @param value   value to mix in
+     * @return new length
+     */
+    static int mixLen(int current, String value) {
+        return checkOverflow(current + value.length());
+    }
+
+    /**
+     * Mix coder into current coder
+     * @param current current coder
+     * @param value   value to mix in
+     * @return new coder
+     */
+    static byte mixCoder(byte current, char value) {
+        return (byte)(current | (StringLatin1.canEncode(value) ? 0 : 1));
+    }
+
+    /**
+     * Mix coder into current coder
+     * @param current current coder
+     * @param value   value to mix in
+     * @return new coder
+     */
+    static byte mixCoder(byte current, String value) {
+        return (byte)(current | value.coder());
+    }
+
+    /**
+     * Mix coder into current coder
+     * @param current current coder
+     * @param value   value to mix in
+     * @return new coder
+     */
+    static byte mixCoder(byte current, boolean value) {
+        // Booleans are represented with Latin1
+        return current;
+    }
+
+    /**
+     * Mix coder into current coder
+     * @param current current coder
+     * @param value   value to mix in
+     * @return new coder
+     */
+    static byte mixCoder(byte current, byte value) {
+        // Bytes are represented with Latin1
+        return current;
+    }
+
+    /**
+     * Mix coder into current coder
+     * @param current current coder
+     * @param value   value to mix in
+     * @return new coder
+     */
+    static byte mixCoder(byte current, short value) {
+        // Shorts are represented with Latin1
+        return current;
+    }
+
+    /**
+     * Mix coder into current coder
+     * @param current current coder
+     * @param value   value to mix in
+     * @return new coder
+     */
+    static byte mixCoder(byte current, int value) {
+        // Ints are represented with Latin1
+        return current;
+    }
+
+    /**
+     * Mix coder into current coder
+     * @param current current coder
+     * @param value   value to mix in
+     * @return new coder
+     */
+    static byte mixCoder(byte current, long value) {
+        // Longs are represented with Latin1
+        return current;
+    }
+
+    /**
+     * Prepends the stringly representation of boolean value into buffer,
+     * given the coder and final index. Index is measured in chars, not in bytes!
+     *
+     * @param index final char index in the buffer
+     * @param buf   buffer to append to
+     * @param coder coder to add with
+     * @param value boolean value to encode
+     * @return new index
+     */
+    static int prepend(int index, byte[] buf, byte coder, boolean value) {
+        if (coder == String.LATIN1) {
+            if (value) {
+                buf[--index] = 'e';
+                buf[--index] = 'u';
+                buf[--index] = 'r';
+                buf[--index] = 't';
+            } else {
+                buf[--index] = 'e';
+                buf[--index] = 's';
+                buf[--index] = 'l';
+                buf[--index] = 'a';
+                buf[--index] = 'f';
+            }
+        } else {
+            if (value) {
+                StringUTF16.putChar(buf, --index, 'e');
+                StringUTF16.putChar(buf, --index, 'u');
+                StringUTF16.putChar(buf, --index, 'r');
+                StringUTF16.putChar(buf, --index, 't');
+            } else {
+                StringUTF16.putChar(buf, --index, 'e');
+                StringUTF16.putChar(buf, --index, 's');
+                StringUTF16.putChar(buf, --index, 'l');
+                StringUTF16.putChar(buf, --index, 'a');
+                StringUTF16.putChar(buf, --index, 'f');
+            }
+        }
+        return index;
+    }
+
+    /**
+     * Prepends the stringly representation of byte value into buffer,
+     * given the coder and final index. Index is measured in chars, not in bytes!
+     *
+     * @param index final char index in the buffer
+     * @param buf   buffer to append to
+     * @param coder coder to add with
+     * @param value byte value to encode
+     * @return new index
+     */
+    static int prepend(int index, byte[] buf, byte coder, byte value) {
+        return prepend(index, buf, coder, (int)value);
+    }
+
+    /**
+     * Prepends the stringly representation of char value into buffer,
+     * given the coder and final index. Index is measured in chars, not in bytes!
+     *
+     * @param index final char index in the buffer
+     * @param buf   buffer to append to
+     * @param coder coder to add with
+     * @param value char value to encode
+     * @return new index
+     */
+    static int prepend(int index, byte[] buf, byte coder, char value) {
+        if (coder == String.LATIN1) {
+            buf[--index] = (byte) (value & 0xFF);
+        } else {
+            StringUTF16.putChar(buf, --index, value);
+        }
+        return index;
+    }
+
+    /**
+     * Prepends the stringly representation of short value into buffer,
+     * given the coder and final index. Index is measured in chars, not in bytes!
+     *
+     * @param index final char index in the buffer
+     * @param buf   buffer to append to
+     * @param coder coder to add with
+     * @param value short value to encode
+     * @return new index
+     */
+    static int prepend(int index, byte[] buf, byte coder, short value) {
+        return prepend(index, buf, coder, (int)value);
+    }
+
+    /**
+     * Prepends the stringly representation of integer value into buffer,
+     * given the coder and final index. Index is measured in chars, not in bytes!
+     *
+     * @param index final char index in the buffer
+     * @param buf   buffer to append to
+     * @param coder coder to add with
+     * @param value integer value to encode
+     * @return new index
+     */
+    static int prepend(int index, byte[] buf, byte coder, int value) {
+        if (coder == String.LATIN1) {
+            return Integer.getChars(value, index, buf);
+        } else {
+            return Integer.getCharsUTF16(value, index, buf);
+        }
+    }
+
+    /**
+     * Prepends the stringly representation of long value into buffer,
+     * given the coder and final index. Index is measured in chars, not in bytes!
+     *
+     * @param index final char index in the buffer
+     * @param buf   buffer to append to
+     * @param coder coder to add with
+     * @param value long value to encode
+     * @return new index
+     */
+    static int prepend(int index, byte[] buf, byte coder, long value) {
+        if (coder == String.LATIN1) {
+            return Long.getChars(value, index, buf);
+        } else {
+            return Long.getCharsUTF16(value, index, buf);
+        }
+    }
+
+    /**
+     * Prepends the stringly representation of String value into buffer,
+     * given the coder and final index. Index is measured in chars, not in bytes!
+     *
+     * @param index final char index in the buffer
+     * @param buf   buffer to append to
+     * @param coder coder to add with
+     * @param value String value to encode
+     * @return new index
+     */
+    static int prepend(int index, byte[] buf, byte coder, String value) {
+        index -= value.length();
+        value.getBytes(buf, index, coder);
+        return index;
+    }
+
+    /**
+     * Instantiates the String with given buffer and coder
+     * @param buf     buffer to use
+     * @param coder   coder to use
+     * @return String resulting string
+     */
+    static String newString(byte[] buf, byte coder) {
+        // Use the private, non-copying constructor (unsafe!)
+        return new String(buf, coder);
+    }
+
+}