org.mmbase.util.ChainedIterator.java Source code

Introduction

Here is the source code for org.mmbase.util.ChainedIterator.java

Source

/*
    
This software is OSI Certified Open Source Software.
OSI Certified is a certification mark of the Open Source Initiative.
    
The license (Mozilla version 1.0) can be read at the MMBase site.
See http://www.MMBase.org/license
    
*/

package org.mmbase.util;

import java.util.*;

/**
 * Like org.apache.commons.collections.iterators.IteratorChain, to avoid the dependency....
 *
 * It is quite easy to understand what this actually is. It is an Iterator implemetnation which is
 * based on other Iterators. During iterating, it simply iterates them all sequentially.
 *
 *
 *
 * @author   Michiel Meeuwissen
 * @since   MMBase-1.8
 * @version $Id: ChainedIterator.java 41055 2010-02-15 23:59:16Z michiel $
 */
public class ChainedIterator<E> implements Iterator<E> {

    private final List<Iterator<E>> iterators = new ArrayList<Iterator<E>>();
    private Iterator<Iterator<E>> iteratorIterator = null;
    private Iterator<E> iterator = null;

    public ChainedIterator() {
    }

    public ChainedIterator(Iterator<E>... is) {
        for (Iterator<E> i : is) {
            iterators.add(i);
        }
    }

    /**
     * Adds another iterator
     * @exception IllegalStateException if iteration already started
     */
    public ChainedIterator<E> addIterator(Iterator<E> i) {
        if (iteratorIterator != null)
            throw new IllegalStateException();
        iterators.add(i);
        return this;
    }

    private void setIterator() {
        while (iteratorIterator.hasNext() && iterator == null) {
            iterator = iteratorIterator.next();
            if (!iterator.hasNext())
                iterator = null;
        }
    }

    private void start() {
        if (iteratorIterator == null) {
            iteratorIterator = iterators.iterator();
            setIterator();
        }
    }

    public boolean hasNext() {
        start();
        return (iterator != null && iterator.hasNext());

    }

    public E next() {
        start();
        if (iterator == null)
            throw new NoSuchElementException();
        E res = iterator.next();
        if (!iterator.hasNext()) {
            iterator = null;
            setIterator();
        }
        return res;

    }

    /**
     * Not supported
     */
    public void remove() {
        throw new UnsupportedOperationException();
    }

    /**
     * Just testing
     */
    public static void main(String argv[]) {
        ChainedIterator<String> it = new ChainedIterator<String>();
        List<String> o = new ArrayList<String>();
        List<String> a = new ArrayList<String>();
        a.add("a");
        a.add("b");
        List<String> b = new ArrayList<String>();
        List<String> c = new ArrayList<String>();
        c.add("c");
        c.add("d");
        List<String> d = new ArrayList<String>();
        it.addIterator(o.iterator());
        it.addIterator(a.iterator());
        it.addIterator(b.iterator());
        it.addIterator(c.iterator());
        it.addIterator(d.iterator());
        while (it.hasNext()) {
            System.out.println("" + it.next());
        }
    }

}