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JWKTL (Java Wiktionary Library) is a Java-based API that enables efficient and structured access to the information encoded in the English and the German Wiktionary edition, including sense definitions, part of speech tags, etymology, example sentences, translations, semantic relations and many other lexical information types.

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/*******************************************************************************
 * Copyright 2013
 * Ubiquitous Knowledge Processing (UKP) Lab
 * Technische Universität Darmstadt
 * 
 * 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 de.tudarmstadt.ukp.jwktl.api.util;

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * Default implementation of the {@link IWiktionaryIterator} interface.
 * @author Christian M. Meyer
 */
public abstract class WiktionaryIterator 
		implements IWiktionaryIterator {

	protected Type nextValue;
	protected boolean closed;

	public Iterator iterator() {
		return this;
	}

	public boolean hasNext() {
		if (closed)
			return false;
		if (nextValue != null)
			return true;

		nextValue = fetchNext();
		if (nextValue == null)
			close(); // Auto-close on exit.
			return (nextValue != null);
	}

	public Type next() {
		if (hasNext()) {
			Type value = nextValue;
			nextValue = null;
			return value;
		} else
			throw new NoSuchElementException();
	}

	/** Hotspot for fetching the next element for iteration. If there are no
	 *  elements left, null is to be returned, which causes the 
	 *  iterator to return false for the next {@link #hasNext()}. */
	protected abstract Type fetchNext();

    /** Hotspot that is invoked after closing the iteration, i.e. either all
     *  items are traversed or manual termination. The hotspot is called only
     *  once. */
	protected abstract void doClose(); 

	public void remove() {
		throw new UnsupportedOperationException("JWKTL access is read-only.");
	}
	
	public void close() {
		if (!closed) {
			doClose();
			closed = true;
		}
	}
	
	public boolean isClosed() {
		return closed;
	}

}