EmptySet.java

/*******************************************************************************
 * Copyright (c) 2013 Stephen F. Siegel, University of Delaware.
 * 
 * This file is part of SARL.
 * 
 * SARL is free software: you can redistribute it and/or modify it under
 * the terms of the GNU Lesser General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or (at your
 * option) any later version.
 * 
 * SARL is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
 * License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with SARL. If not, see <http://www.gnu.org/licenses/>.
 ******************************************************************************/
package edu.udel.cis.vsl.sarl.util;

import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.Set;

/** An immutable, empty set. */
public class EmptySet<E> implements Set<E> {

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

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

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

	@Override
	public Iterator<E> iterator() {
		return new EmptyIterator<E>();
	}

	@Override
	public Object[] toArray() {
		return new Object[0];
	}

	@Override
	public <T> T[] toArray(T[] a) {
		if (a.length == 0)
			return a;
		return Arrays.copyOf(a, 0);
	}

	@Override
	public boolean add(E e) {
		throw new UnsupportedOperationException("This is an immutable set");
	}

	@Override
	public boolean remove(Object o) {
		throw new UnsupportedOperationException("This is an immutable set");
	}

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

	@Override
	public boolean addAll(Collection<? extends E> c) {
		throw new UnsupportedOperationException("This is an immutable set");
	}

	@Override
	public boolean retainAll(Collection<?> c) {
		throw new UnsupportedOperationException("This is an immutable set");
	}

	@Override
	public boolean removeAll(Collection<?> c) {
		throw new UnsupportedOperationException("This is an immutable set");
	}

	@Override
	public void clear() {
		throw new UnsupportedOperationException("This is an immutable set");
	}

}