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'databene commons' is an open source Java library by Volker Bergmann. It provides extensions to the Java core library by utility classes, abstract concepts and concrete implementations.

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/*
 * Copyright (C) 2004-2015 Volker Bergmann ([email protected]).
 * All rights reserved.
 *
 * 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 org.databene.commons.iterator;

import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.Stack;

/**
 * Allows linear iteration over nested {@link Set}s using a plain {@link Iterator}.
 * Created: 04.08.2013 07:58:05
 * @param  the type to iterate
 * @since 0.5.24
 * @author Volker Bergmann
 */

public class RecursiveMapValueIterator implements Iterator {
	
	private Stack> iterators;
	private E next;
	private boolean hasNext;
	
	public RecursiveMapValueIterator(Map root) {
		this.iterators = new Stack>();
		this.iterators.push(root.values().iterator());
		forward();
	}

	@Override
	public boolean hasNext() {
		return hasNext;
	}

	@Override
	public E next() {
		E result = next;
		forward();
		return result;
	}

	@Override
	public void remove() {
		iterators.peek().remove();
	}
	
	@SuppressWarnings("unchecked")
	private void forward() {
		Iterator iterator = iterators.peek();
		if (iterator.hasNext()) {
			Object candidate = iterator.next();
			if (candidate instanceof Map) {
				iterators.push(((Map) candidate).values().iterator());
				forward();
			} else {
				hasNext = true;
				next = (E) candidate;
			}
		} else if (iterators.size() > 1) {
			iterators.pop();
			forward();
		} else {
			this.hasNext = false;
			this.next = null;
		}
	}

}