WhileClosure.java

/*
 *  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.functors;

import java.io.Serializable;

import org.apache.commons.collections.Closure;
import org.apache.commons.collections.Predicate;

/**
 * Closure implementation that executes a closure repeatedly until a condition is met,
 * like a do-while or while loop.
 * 
 * @since Commons Collections 3.0
 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
 *
 * @author Stephen Colebourne
 */
public class WhileClosure implements Closure, Serializable {

    /** Serial version UID */
    private static final long serialVersionUID = -3110538116913760108L;

    /** The test condition */
    private final Predicate iPredicate;
    /** The closure to call */
    private final Closure iClosure;
    /** The flag, true is a do loop, false is a while */
    private final boolean iDoLoop;

    /**
     * Factory method that performs validation.
     * 
     * @param predicate  the predicate used to evaluate when the loop terminates, not null
     * @param closure  the closure the execute, not null
     * @param doLoop  true to act as a do-while loop, always executing the closure once
     * @return the <code>while</code> closure
     * @throws IllegalArgumentException if the predicate or closure is null
     */
    public static Closure getInstance(Predicate predicate, Closure closure, boolean doLoop) {
        if (predicate == null) {
            throw new IllegalArgumentException("Predicate must not be null");
        }
        if (closure == null) {
            throw new IllegalArgumentException("Closure must not be null");
        }
        return new WhileClosure(predicate, closure, doLoop);
    }

    /**
     * Constructor that performs no validation.
     * Use <code>getInstance</code> if you want that.
     * 
     * @param predicate  the predicate used to evaluate when the loop terminates, not null
     * @param closure  the closure the execute, not null
     * @param doLoop  true to act as a do-while loop, always executing the closure once
     */
    public WhileClosure(Predicate predicate, Closure closure, boolean doLoop) {
        super();
        iPredicate = predicate;
        iClosure = closure;
        iDoLoop = doLoop;
    }

    /**
     * Executes the closure until the predicate is false.
     * 
     * @param input  the input object
     */
    public void execute(Object input) {
        if (iDoLoop) {
            iClosure.execute(input);
        }
        while (iPredicate.evaluate(input)) {
            iClosure.execute(input);
        }
    }

    /**
     * Gets the predicate in use.
     * 
     * @return the predicate
     * @since Commons Collections 3.1
     */
    public Predicate getPredicate() {
        return iPredicate;
    }

    /**
     * Gets the closure.
     * 
     * @return the closure
     * @since Commons Collections 3.1
     */
    public Closure getClosure() {
        return iClosure;
    }

    /**
     * Is the loop a do-while loop.
     * 
     * @return true is do-while, false if while
     * @since Commons Collections 3.1
     */
    public boolean isDoLoop() {
        return iDoLoop;
    }

}