/*
 * Copyright (C) 2008 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 javax.annotation.Nullable;

import com.google.common.annotations.GwtCompatible;

/**
 * Bimap with no mappings.
 *
 * @author Jared Levy
 */
@GwtCompatible(emulated = true)
@SuppressWarnings("serial") // uses writeReplace(), not default serialization
final class EmptyImmutableBiMap extends ImmutableBiMap<Object, Object> {
	static final EmptyImmutableBiMap INSTANCE = new EmptyImmutableBiMap();

	private EmptyImmutableBiMap() {
	}

	@Override
	public ImmutableBiMap<Object, Object> inverse() {
		return this;
	}

	@Override
	public int size() {
		return 0;
	}

	@Override
	public boolean isEmpty() {
		return true;
	}

	@Override
	public Object get(@Nullable Object key) {
		return null;
	}

	@Override
	public ImmutableSet<Entry<Object, Object>> entrySet() {
		return ImmutableSet.of();
	}

	@Override
	ImmutableSet<Entry<Object, Object>> createEntrySet() {
		throw new AssertionError("should never be called");
	}

	@Override
	public ImmutableSetMultimap<Object, Object> asMultimap() {
		return ImmutableSetMultimap.of();
	}

	@Override
	public ImmutableSet<Object> keySet() {
		return ImmutableSet.of();
	}

	@Override
	boolean isPartialView() {
		return false;
	}

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