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Groovy: A powerful, dynamic language for the JVM

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/*
 * Copyright 2003-2007 the original author or 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 groovy.util.slurpersupport;

import java.util.Iterator;

/**
 * @author John Wilson
 *
 */
public abstract class NodeIterator implements Iterator {
    private static final Object DELAYED_INIT = new Object();
    private final Iterator iter;
    private Object nextNode;

    public NodeIterator(final Iterator iter) {
        this.iter = iter;
        this.nextNode = DELAYED_INIT;
    }

    private void initNextNode(){
        if (nextNode==DELAYED_INIT) nextNode = getNextNode(iter);
    }

    public boolean hasNext() {
        initNextNode();
        return this.nextNode != null;
    }

    public Object next() {
        initNextNode();
        try {
            return this.nextNode;
        } finally {
            this.nextNode = getNextNode(this.iter);
        }
    }

    public void remove() {
        throw new UnsupportedOperationException();
    }

    protected abstract Object getNextNode(final Iterator iter);
}