Utils.java Source code

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/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright 1997-2007 Sun Microsystems, Inc. All rights reserved.
 *
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common
 * Development and Distribution License("CDDL") (collectively, the
 * "License"). You may not use this file except in compliance with the
 * License. You can obtain a copy of the License at
 * http://www.netbeans.org/cddl-gplv2.html
 * or nbbuild/licenses/CDDL-GPL-2-CP. See the License for the
 * specific language governing permissions and limitations under the
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 * Notice in each file and include the License file at
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 * particular file as subject to the "Classpath" exception as provided
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 * accompanied this code. If applicable, add the following below the
 * License Header, with the fields enclosed by brackets [] replaced by
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 * Contributor(s):
 *
 * The Original Software is NetBeans. The Initial Developer of the Original
 * Software is Sun Microsystems, Inc. Portions Copyright 1997-2006 Sun
 * Microsystems, Inc. All Rights Reserved.
 *
 * If you wish your version of this file to be governed by only the CDDL
 * or only the GPL Version 2, indicate your decision by adding
 * "[Contributor] elects to include this software in this distribution
 * under the [CDDL or GPL Version 2] license." If you do not indicate a
 * single choice of license, a recipient has the option to distribute
 * your version of this file under either the CDDL, the GPL Version 2 or
 * to extend the choice of license to its licensees as provided above.
 * However, if you add GPL Version 2 code and therefore, elected the GPL
 * Version 2 license, then the option applies only if the new code is
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 */

import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * @since 4.37
 * @author Jaroslav Tulach
 */

public class Utils {
    /**
     * Concatenates the content of two enumerations into one.
     * Until the
     * end of <code>en1</code> is reached its elements are being served.
     * As soon as the <code>en1</code> has no more elements, the content
     * of <code>en2</code> is being returned.
     *
     * @param en1 first enumeration
     * @param en2 second enumeration
     * @return enumeration
     */
    public static <T> Enumeration<T> concat(Enumeration<? extends T> en1, Enumeration<? extends T> en2) {
        ArrayList<Enumeration<? extends T>> two = new ArrayList<Enumeration<? extends T>>();
        two.add(en1);
        two.add(en2);
        return new SeqEn<T>(Collections.enumeration(two));
    }

}

class SeqEn<T> extends Object implements Enumeration<T> {
    /** enumeration of Enumerations */
    private Enumeration<? extends Enumeration<? extends T>> en;

    /** current enumeration */
    private Enumeration<? extends T> current;

    /** is {@link #current} up-to-date and has more elements?
    * The combination <CODE>current == null</CODE> and
    * <CODE>checked == true means there are no more elements
    * in this enumeration.
    */
    private boolean checked = false;

    /** Constructs new enumeration from already existing. The elements
    * of <CODE>en</CODE> should be also enumerations. The resulting
    * enumeration contains elements of such enumerations.
    *
    * @param en enumeration of Enumerations that should be sequenced
    */
    public SeqEn(Enumeration<? extends Enumeration<? extends T>> en) {
        this.en = en;
    }

    /** Ensures that current enumeration is set. If there aren't more
    * elements in the Enumerations, sets the field <CODE>current</CODE> to null.
    */
    private void ensureCurrent() {
        while ((current == null) || !current.hasMoreElements()) {
            if (en.hasMoreElements()) {
                current = en.nextElement();
            } else {
                // no next valid enumeration
                current = null;

                return;
            }
        }
    }

    /** @return true if we have more elements */
    public boolean hasMoreElements() {
        if (!checked) {
            ensureCurrent();
            checked = true;
        }

        return current != null;
    }

    /** @return next element
    * @exception NoSuchElementException if there is no next element
    */
    public T nextElement() {
        if (!checked) {
            ensureCurrent();
        }

        if (current != null) {
            checked = false;

            return current.nextElement();
        } else {
            checked = true;
            throw new java.util.NoSuchElementException();
        }
    }
}