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Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. Guava has only one code dependency - javax.annotation, per the JSR-305 spec.

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/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Objects;

import java.util.Map.Entry;

import javax.annotation.Nullable;

/**
 * Implementation of the {@code equals}, {@code hashCode}, and {@code toString}
 * methods of {@code Entry}.
 *
 * @author Jared Levy
 */
@GwtCompatible
abstract class AbstractMapEntry implements Entry {

  @Override
  public abstract K getKey();

  @Override
  public abstract V getValue();

  @Override
  public V setValue(V value) {
    throw new UnsupportedOperationException();
  }

  @Override public boolean equals(@Nullable Object object) {
    if (object instanceof Entry) {
      Entry that = (Entry) object;
      return Objects.equal(this.getKey(), that.getKey())
          && Objects.equal(this.getValue(), that.getValue());
    }
    return false;
  }

  @Override public int hashCode() {
    K k = getKey();
    V v = getValue();
    return ((k == null) ? 0 : k.hashCode()) ^ ((v == null) ? 0 : v.hashCode());
  }

  /**
   * Returns a string representation of the form {@code {key}={value}}.
   */
  @Override public String toString() {
    return getKey() + "=" + getValue();
  }
}