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+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// http://code.google.com/p/protobuf/
+//
+// 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.List;
+import java.util.AbstractList;
+import java.util.ArrayList;
+import java.util.RandomAccess;
+import java.util.Collection;
+
+/**
+ * An implementation of {@link LazyStringList} that wraps an ArrayList. Each
+ * element is either a ByteString or a String. It caches the last one requested
+ * which is most likely the one needed next. This minimizes memory usage while
+ * satisfying the most common use cases.
+ * <p>
+ * <strong>Note that this implementation is not synchronized.</strong>
+ * If multiple threads access an <tt>ArrayList</tt> instance concurrently,
+ * and at least one of the threads modifies the list structurally, it
+ * <i>must</i> be synchronized externally.  (A structural modification is
+ * any operation that adds or deletes one or more elements, or explicitly
+ * resizes the backing array; merely setting the value of an element is not
+ * a structural modification.)  This is typically accomplished by
+ * synchronizing on some object that naturally encapsulates the list.
+ * <p>
+ * If the implementation is accessed via concurrent reads, this is thread safe.
+ * Conversions are done in a thread safe manner. It's possible that the
+ * conversion may happen more than once if two threads attempt to access the
+ * same element and the modifications were not visible to each other, but this
+ * will not result in any corruption of the list or change in behavior other
+ * than performance.
+ *
+ * @author jonp@google.com (Jon Perlow)
+ */
+public class LazyStringArrayList extends AbstractList<String>
+    implements LazyStringList, RandomAccess {
+
+  public final static LazyStringList EMPTY = new UnmodifiableLazyStringList(
+      new LazyStringArrayList());
+
+  private final List<Object> list;
+
+  public LazyStringArrayList() {
+    list = new ArrayList<Object>();
+  }
+
+  public LazyStringArrayList(List<String> from) {
+    list = new ArrayList<Object>(from);
+  }
+
+  @Override
+  public String get(int index) {
+    Object o = list.get(index);
+    if (o instanceof String) {
+      return (String) o;
+    } else {
+      ByteString bs = (ByteString) o;
+      String s = bs.toStringUtf8();
+      if (Internal.isValidUtf8(bs)) {
+        list.set(index, s);
+      }
+      return s;
+    }
+  }
+
+  @Override
+  public int size() {
+    return list.size();
+  }
+
+  @Override
+  public String set(int index, String s) {
+    Object o = list.set(index, s);
+    return asString(o);
+  }
+
+  @Override
+  public void add(int index, String element) {
+    list.add(index, element);
+    modCount++;
+  }
+
+  @Override
+  public boolean addAll(int index, Collection<? extends String> c) {
+    boolean ret = list.addAll(index, c);
+    modCount++;
+    return ret;
+  }
+
+  @Override
+  public String remove(int index) {
+    Object o = list.remove(index);
+    modCount++;
+    return asString(o);
+  }
+
+  public void clear() {
+    list.clear();
+    modCount++;
+  }
+
+  // @Override
+  public void add(ByteString element) {
+    list.add(element);
+    modCount++;
+  }
+
+  // @Override
+  public ByteString getByteString(int index) {
+    Object o = list.get(index);
+    if (o instanceof String) {
+      ByteString b = ByteString.copyFromUtf8((String) o);
+      list.set(index, b);
+      return b;
+    } else {
+      return (ByteString) o;
+    }
+  }
+
+  private String asString(Object o) {
+    if (o instanceof String) {
+      return (String) o;
+    } else {
+      return ((ByteString) o).toStringUtf8();
+    }
+  }
+}