Collections.java

/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You 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.
 *  
 *  CHANGES:
 *  Copied from http://www.java2s.com/Open-Source/Android/android-core/platform-libcore/java/util/Collections.java.htm
 *	Changed package
 */

package com.robotoworks.mechanoid.internal.util;

import java.io.Serializable;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

public class Collections {
    public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) {
        if (map.isEmpty()) {
            return new SetFromMap<E>(map);
        }
        throw new IllegalArgumentException();
    }
    
	private static class SetFromMap<E> extends AbstractSet<E> implements Serializable {
		private static final long serialVersionUID = 2454657854757543876L;

		// must named as it, to pass serialization compatibility test.
		private Map<E, Boolean> m;

		private transient Set<E> backingSet;

		SetFromMap(final Map<E, Boolean> map) {
			super();
			m = map;
			backingSet = map.keySet();
		}

		@Override
		public boolean equals(Object object) {
			return backingSet.equals(object);
		}

		@Override
		public int hashCode() {
			return backingSet.hashCode();
		}

		@Override
		public boolean add(E object) {
			return m.put(object, Boolean.TRUE) == null;
		}

		@Override
		public void clear() {
			m.clear();
		}

		@Override
		public String toString() {
			return backingSet.toString();
		}

		@Override
		public boolean contains(Object object) {
			return backingSet.contains(object);
		}

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

		@Override
		public boolean isEmpty() {
			return m.isEmpty();
		}

		@Override
		public boolean remove(Object object) {
			return m.remove(object) != null;
		}

		@Override
		public boolean retainAll(Collection<?> collection) {
			return backingSet.retainAll(collection);
		}

		@Override
		public Object[] toArray() {
			return backingSet.toArray();
		}

		@Override
		public <T> T[] toArray(T[] contents) {
			return backingSet.toArray(contents);
		}

		@Override
		public Iterator<E> iterator() {
			return backingSet.iterator();
		}

		@Override
		public int size() {
			return m.size();
		}
	}
}