trunk/proposal/sandbox/junit/src/main/org/apache/tools/ant/taskdefs/optional/rjunit/CompoundEnumeration.java

/*
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2002 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution, if
 *    any, must include the following acknowlegement:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowlegement may appear in the software itself,
 *    if and wherever such third-party acknowlegements normally appear.
 *
 * 4. The names "The Jakarta Project", "Ant", and "Apache Software
 *    Foundation" must not be used to endorse or promote products derived
 *    from this software without prior written permission. For written
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache"
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 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */
package org.apache.tools.ant.taskdefs.optional.rjunit;

import java.util.Enumeration;
import java.util.NoSuchElementException;

/**
 * Convenient enumeration over an array of enumeration. For example:
 * <pre>
 * Enumeration e1 = v1.elements();
 * while (e1.hasMoreElements()){
 *    // do something
 * }
 * Enumeration e2 = v2.elements();
 * while (e2.hasMoreElements()){
 *    // do the same thing
 * }
 * </pre>
 * can be written as:
 * <pre>
 * Enumeration[] enums = { v1.elements(), v2.elements() };
 * Enumeration e = Enumerations.fromCompound(enums);
 * while (e.hasMoreElements()){
 *    // do something
 * }
 * </pre>
 * Note that the enumeration will skip null elements in the array. The following is
 * thus possible:
 * <pre>
 * Enumeration[] enums = { v1.elements(), null, v2.elements() }; // a null enumeration in the array
 * Enumeration e = Enumerations.fromCompound(enums);
 * while (e.hasMoreElements()){
 *    // do something
 * }
 * </pre>
 */
public class CompoundEnumeration implements Enumeration {

    /** enumeration array */
    private Enumeration[] enumArray;

    /** index in the enums array */
    private int index = 0;

    public CompoundEnumeration(Enumeration[] enumarray) {
        this.enumArray = enumarray;
    }

    /**
     * Tests if this enumeration contains more elements.
     *
     * @return  <code>true</code> if and only if this enumeration object
     *           contains at least one more element to provide;
     *          <code>false</code> otherwise.
     */
    public boolean hasMoreElements() {
        while (index < enumArray.length) {
            if (enumArray[index] != null && enumArray[index].hasMoreElements()) {
                return true;
            }
            index++;
        }
        return false;
    }

    /**
     * Returns the next element of this enumeration if this enumeration
     * object has at least one more element to provide.
     *
     * @return     the next element of this enumeration.
     * @throws  NoSuchElementException  if no more elements exist.
     */
    public Object nextElement() throws NoSuchElementException {
        if (hasMoreElements()) {
            return enumArray[index].nextElement();
        }
        throw new NoSuchElementException();
    }
}