EmptyImmutableMultiset.java

/*
 * Copyright (C) 2008 Google Inc.
 *
 * 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;

/**
 * An empty immutable multiset.
 * 
 * @author Jared Levy
 */
@GwtCompatible(serializable = true)
final class EmptyImmutableMultiset extends ImmutableMultiset<Object> {
  static final EmptyImmutableMultiset INSTANCE = new EmptyImmutableMultiset();

  private EmptyImmutableMultiset() {
    super(ImmutableMap.<Object, Integer>of(), 0);
  }

  Object readResolve() {
    return INSTANCE; // preserve singleton property
  }

  private static final long serialVersionUID = 0;
}