CompositeIterator.java

/*******************************************************************************
 * Copyright (c) 1998, 2015 Oracle and/or its affiliates. All rights reserved.
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0
 * which accompanies this distribution.
 * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *     Oracle - initial API and implementation from Oracle TopLink
******************************************************************************/
package org.eclipse.persistence.tools.workbench.utility.iterators;

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

import org.eclipse.persistence.tools.workbench.utility.ClassTools;


/**
 * A <code>CompositeIterator</code> wraps a collection
 * of <code>Iterator</code>s and makes them appear to be a single
 * <code>Iterator</code>.
 */
public class CompositeIterator implements Iterator {
    private final Iterator iterators;
    private Iterator currentIterator;
    private Iterator lastIteratorToReturnNext;


    /**
     * Construct an iterator with the specified collection of iterators.
     */
    public CompositeIterator(Collection iterators) {
        this(iterators.iterator());
    }

    /**
     * Construct an iterator with the specified collection of iterators.
     */
    public CompositeIterator(Iterator iterators) {
        super();
        this.iterators = iterators;
    }

    /**
     * Construct an iterator with the specified object prepended
     * to the specified iterator.
     */
    public CompositeIterator(Object object, Iterator iterator) {
        this(new SingleElementIterator(object), iterator);
    }

    /**
     * Construct an iterator with the specified object appended
     * to the specified iterator.
     */
    public CompositeIterator(Iterator iterator, Object object) {
        this(iterator, new SingleElementIterator(object));
    }

    /**
     * Construct an iterator with the specified iterators.
     */
    public CompositeIterator(Iterator iterator1, Iterator iterator2) {
        this(new ArrayIterator(new Object[] {iterator1, iterator2}));
    }

    /**
     * Construct an iterator with the specified iterators.
     */
    public CompositeIterator(Iterator iterator1, Iterator iterator2, Iterator iterator3) {
        this(new ArrayIterator(new Object[] {iterator1, iterator2, iterator3}));
    }

    /**
     * Construct an iterator with the specified array of iterators.
     */
    public CompositeIterator(Iterator[] iterators) {
        this(new ArrayIterator(iterators));
    }

    /**
     * @see java.util.Iterator#hasNext()
     */
    public boolean hasNext() {
        try {
            this.loadCurrentIterator();
        } catch (NoSuchElementException ex) {
            // this occurs if there are no iterators at all
            return false;
        }
        return this.currentIterator.hasNext();
    }

    /**
     * @see java.util.Iterator#next()
     */
    public Object next() {
        this.loadCurrentIterator();
        Object result = this.currentIterator.next();

        // the statement above will throw a NoSuchElementException
        // if the current iterator is at the end of the line;
        // so if we get here, we can set 'lastIteratorToReturnNext'
        this.lastIteratorToReturnNext = this.currentIterator;

        return result;
    }

    /**
     * @see java.util.Iterator#remove()
     */
    public void remove() {
        if (this.lastIteratorToReturnNext == null) {
            // CompositeIterator#next() has never been called
            throw new IllegalStateException();
        }
        this.lastIteratorToReturnNext.remove();
    }

    /**
     * Load currentIterator with the first iterator that <code>hasNext()</code>
     * or the final iterator if all the elements have already been retrieved.
     */
    private void loadCurrentIterator() {
        if (this.currentIterator == null) {
            this.currentIterator = (Iterator) this.iterators.next();
        }
        while (( ! this.currentIterator.hasNext()) && this.iterators.hasNext()) {
            this.currentIterator = (Iterator) this.iterators.next();
        }
    }

    /**
     * @see java.lang.Object#toString()
     */
    public String toString() {
        return ClassTools.shortClassNameForObject(this) + '(' + this.iterators + ')';
    }

}