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diff --git a/java/src/main/java/com/google/protobuf/BoundedByteString.java b/java/src/main/java/com/google/protobuf/BoundedByteString.java
new file mode 100644
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--- /dev/null
+++ b/java/src/main/java/com/google/protobuf/BoundedByteString.java
@@ -0,0 +1,163 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.util.NoSuchElementException;
+
+/**
+ * This class is used to represent the substring of a {@link ByteString} over a
+ * single byte array. In terms of the public API of {@link ByteString}, you end
+ * up here by calling {@link ByteString#copyFrom(byte[])} followed by {@link
+ * ByteString#substring(int, int)}.
+ *
+ * <p>This class contains most of the overhead involved in creating a substring
+ * from a {@link LiteralByteString}.  The overhead involves some range-checking
+ * and two extra fields.
+ *
+ * @author carlanton@google.com (Carl Haverl)
+ */
+class BoundedByteString extends LiteralByteString {
+
+  private final int bytesOffset;
+  private final int bytesLength;
+
+  /**
+   * Creates a {@code BoundedByteString} backed by the sub-range of given array,
+   * without copying.
+   *
+   * @param bytes  array to wrap
+   * @param offset index to first byte to use in bytes
+   * @param length number of bytes to use from bytes
+   * @throws IllegalArgumentException if {@code offset < 0}, {@code length < 0},
+   *                                  or if {@code offset + length >
+   *                                  bytes.length}.
+   */
+  BoundedByteString(byte[] bytes, int offset, int length) {
+    super(bytes);
+    if (offset < 0) {
+      throw new IllegalArgumentException("Offset too small: " + offset);
+    }
+    if (length < 0) {
+      throw new IllegalArgumentException("Length too small: " + offset);
+    }
+    if ((long) offset + length > bytes.length) {
+      throw new IllegalArgumentException(
+          "Offset+Length too large: " + offset + "+" + length);
+    }
+
+    this.bytesOffset = offset;
+    this.bytesLength = length;
+  }
+
+  /**
+   * Gets the byte at the given index.
+   * Throws {@link ArrayIndexOutOfBoundsException}
+   * for backwards-compatibility reasons although it would more properly be
+   * {@link IndexOutOfBoundsException}.
+   *
+   * @param index index of byte
+   * @return the value
+   * @throws ArrayIndexOutOfBoundsException {@code index} is < 0 or >= size
+   */
+  @Override
+  public byte byteAt(int index) {
+    // We must check the index ourselves as we cannot rely on Java array index
+    // checking for substrings.
+    if (index < 0) {
+      throw new ArrayIndexOutOfBoundsException("Index too small: " + index);
+    }
+    if (index >= size()) {
+      throw new ArrayIndexOutOfBoundsException(
+          "Index too large: " + index + ", " + size());
+    }
+
+    return bytes[bytesOffset + index];
+  }
+
+  @Override
+  public int size() {
+    return bytesLength;
+  }
+
+  @Override
+  protected int getOffsetIntoBytes() {
+    return bytesOffset;
+  }
+
+  // =================================================================
+  // ByteString -> byte[]
+
+  @Override
+  protected void copyToInternal(byte[] target, int sourceOffset, 
+      int targetOffset, int numberToCopy) {
+    System.arraycopy(bytes, getOffsetIntoBytes() + sourceOffset, target,
+        targetOffset, numberToCopy);
+  }
+
+  // =================================================================
+  // ByteIterator
+
+  @Override
+  public ByteIterator iterator() {
+    return new BoundedByteIterator();
+  }
+
+  private class BoundedByteIterator implements ByteIterator {
+
+    private int position;
+    private final int limit;
+
+    private BoundedByteIterator() {
+      position = getOffsetIntoBytes();
+      limit = position + size();
+    }
+
+    public boolean hasNext() {
+      return (position < limit);
+    }
+
+    public Byte next() {
+      // Boxing calls Byte.valueOf(byte), which does not instantiate.
+      return nextByte();
+    }
+
+    public byte nextByte() {
+      if (position >= limit) {
+        throw new NoSuchElementException();
+      }
+      return bytes[position++];
+    }
+
+    public void remove() {
+      throw new UnsupportedOperationException();
+    }
+  }
+}