/*
 * 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 java.util.Collection;
import java.util.Set;

import javax.annotation.Nullable;

import com.google.common.annotations.GwtCompatible;

/**
 * An empty immutable set.
 *
 * @author Kevin Bourrillion
 */
@GwtCompatible(serializable = true, emulated = true)
final class EmptyImmutableSet extends ImmutableSet<Object> {
	static final EmptyImmutableSet INSTANCE = new EmptyImmutableSet();

	private EmptyImmutableSet() {
	}

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

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

	@Override
	public boolean contains(@Nullable Object target) {
		return false;
	}

	@Override
	public boolean containsAll(Collection<?> targets) {
		return targets.isEmpty();
	}

	@Override
	public UnmodifiableIterator<Object> iterator() {
		return Iterators.emptyIterator();
	}

	@Override
	boolean isPartialView() {
		return false;
	}

	@Override
	int copyIntoArray(Object[] dst, int offset) {
		return offset;
	}

	@Override
	public ImmutableList<Object> asList() {
		return ImmutableList.of();
	}

	@Override
	public boolean equals(@Nullable Object object) {
		if (object instanceof Set) {
			Set<?> that = (Set<?>) object;
			return that.isEmpty();
		}
		return false;
	}

	@Override
	public final int hashCode() {
		return 0;
	}

	@Override
	boolean isHashCodeFast() {
		return true;
	}

	@Override
	public String toString() {
		return "[]";
	}

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

	private static final long serialVersionUID = 0;
}
