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Commons Collections example source code file (FilterIterator.java)

This example Commons Collections source code file (FilterIterator.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons Collections tags/keywords

filteriterator, filteriterator, illegalstateexception, iterator, iterator, nosuchelementexception, object, object, predicate, predicate, util

The Commons Collections FilterIterator.java source code

/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You 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.apache.commons.collections.iterators;

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

import org.apache.commons.collections.Predicate;

/** 
 * Decorates another {@link Iterator} using a predicate to filter elements.
 * <p>
 * This iterator decorates the underlying iterator, only allowing through
 * those elements that match the specified {@link Predicate Predicate}.
 *
 * @since Commons Collections 1.0
 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
 * 
 * @author James Strachan
 * @author Jan Sorensen
 * @author Ralph Wagner
 * @author Stephen Colebourne
 */
public class FilterIterator implements Iterator {

    /** The iterator being used */
    private Iterator iterator;
    /** The predicate being used */
    private Predicate predicate;
    /** The next object in the iteration */
    private Object nextObject;
    /** Whether the next object has been calculated yet */
    private boolean nextObjectSet = false;

    //-----------------------------------------------------------------------
    /**
     * Constructs a new <code>FilterIterator that will not function
     * until {@link #setIterator(Iterator) setIterator} is invoked.
     */
    public FilterIterator() {
        super();
    }

    /**
     * Constructs a new <code>FilterIterator that will not function
     * until {@link #setPredicate(Predicate) setPredicate} is invoked.
     *
     * @param iterator  the iterator to use
     */
    public FilterIterator(Iterator iterator) {
        super();
        this.iterator = iterator;
    }

    /**
     * Constructs a new <code>FilterIterator that will use the
     * given iterator and predicate.
     *
     * @param iterator  the iterator to use
     * @param predicate  the predicate to use
     */
    public FilterIterator(Iterator iterator, Predicate predicate) {
        super();
        this.iterator = iterator;
        this.predicate = predicate;
    }

    //-----------------------------------------------------------------------
    /** 
     * Returns true if the underlying iterator contains an object that 
     * matches the predicate.
     *
     * @return true if there is another object that matches the predicate
     * @throws NullPointerException if either the iterator or predicate are null
     */
    public boolean hasNext() {
        if (nextObjectSet) {
            return true;
        } else {
            return setNextObject();
        }
    }

    /** 
     * Returns the next object that matches the predicate.
     *
     * @return the next object which matches the given predicate
     * @throws NullPointerException if either the iterator or predicate are null
     * @throws NoSuchElementException if there are no more elements that
     *  match the predicate 
     */
    public Object next() {
        if (!nextObjectSet) {
            if (!setNextObject()) {
                throw new NoSuchElementException();
            }
        }
        nextObjectSet = false;
        return nextObject;
    }

    /**
     * Removes from the underlying collection of the base iterator the last
     * element returned by this iterator.
     * This method can only be called
     * if <code>next() was called, but not after
     * <code>hasNext(), because the hasNext() call
     * changes the base iterator.
     *
     * @throws IllegalStateException if <code>hasNext() has already
     *  been called.
     */
    public void remove() {
        if (nextObjectSet) {
            throw new IllegalStateException("remove() cannot be called");
        }
        iterator.remove();
    }

    //-----------------------------------------------------------------------
    /** 
     * Gets the iterator this iterator is using.
     *
     * @return the iterator
     */
    public Iterator getIterator() {
        return iterator;
    }

    /** 
     * Sets the iterator for this iterator to use.
     * If iteration has started, this effectively resets the iterator.
     *
     * @param iterator  the iterator to use
     */
    public void setIterator(Iterator iterator) {
        this.iterator = iterator;
        nextObject = null;
        nextObjectSet = false;
    }

    //-----------------------------------------------------------------------
    /** 
     * Gets the predicate this iterator is using.
     *
     * @return the predicate
     */
    public Predicate getPredicate() {
        return predicate;
    }

    /** 
     * Sets the predicate this the iterator to use.
     *
     * @param predicate  the predicate to use
     */
    public void setPredicate(Predicate predicate) {
        this.predicate = predicate;
        nextObject = null;
        nextObjectSet = false;
    }

    //-----------------------------------------------------------------------
    /**
     * Set nextObject to the next object. If there are no more 
     * objects then return false. Otherwise, return true.
     */
    private boolean setNextObject() {
        while (iterator.hasNext()) {
            Object object = iterator.next();
            if (predicate.evaluate(object)) {
                nextObject = object;
                nextObjectSet = true;
                return true;
            }
        }
        return false;
    }

}

Other Commons Collections examples (source code examples)

Here is a short list of links related to this Commons Collections FilterIterator.java source code file:



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