enum.java

来自「JAVA 文章管理系统源码」· Java 代码 · 共 596 行 · 第 1/2 页

/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2002-2003 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 acknowledgement:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgement may appear in the software itself,
 *    if and wherever such third-party acknowledgements normally appear.
 *
 * 4. The names "The Jakarta Project", "Commons", 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 [e-mail].
 *
 * 5. Products derived from this software may not be called "Apache"
 *    nor may "Apache" appear in their names without prior written
 *    permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * 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.commons.lang.enum;

import java.io.Serializable;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import org.apache.commons.lang.ClassUtils;
import org.apache.commons.lang.StringUtils;

/**
 * <p>Abstract superclass for type-safe enums.</p>
 *
 * <p>One feature of the C programming language lacking in Java is enumerations. The
 * C implementation based on ints was poor and open to abuse. The original Java
 * recommendation and most of the JDK also uses int constants. It has been recognised
 * however that a more robust type-safe class-based solution can be designed. This
 * class follows the basic Java type-safe enumeration pattern.</p>
 *
 * <p><em>NOTE:</em>Due to the way in which Java ClassLoaders work, comparing
 * Enum objects should always be done using <code>equals()</code>, not <code>==</code>.
 * The equals() method will try == first so in most cases the effect is the same.</p>
 * 
 * <p>Of course, if you actually want (or don't mind) Enums in different class
 * loaders being non-equal, then you can use <code>==</code>.</p>
 * 
 * <h4>Simple Enums</h4>
 *
 * <p>To use this class, it must be subclassed. For example:</p>
 *
 * <pre>
 * public final class ColorEnum extends Enum {
 *   public static final ColorEnum RED = new ColorEnum("Red");
 *   public static final ColorEnum GREEN = new ColorEnum("Green");
 *   public static final ColorEnum BLUE = new ColorEnum("Blue");
 *
 *   private ColorEnum(String color) {
 *     super(color);
 *   }
 * 
 *   public static ColorEnum getEnum(String color) {
 *     return (ColorEnum) getEnum(ColorEnum.class, color);
 *   }
 * 
 *   public static Map getEnumMap() {
 *     return getEnumMap(ColorEnum.class);
 *   }
 * 
 *   public static List getEnumList() {
 *     return getEnumList(ColorEnum.class);
 *   }
 * 
 *   public static Iterator iterator() {
 *     return iterator(ColorEnum.class);
 *   }
 * }
 * </pre>
 *
 * <p>As shown, each enum has a name. This can be accessed using <code>getName</code>.</p>
 *
 * <p>The <code>getEnum</code> and <code>iterator</code> methods are recommended.
 * Unfortunately, Java restrictions require these to be coded as shown in each subclass.
 * An alternative choice is to use the {@link EnumUtils} class.</p>
 * 
 * <h4>Subclassed Enums</h4>
 * <p>A hierarchy of Enum classes can be built. In this case, the superclass is
 * unaffected by the addition of subclasses (as per normal Java). The subclasses
 * may add additional Enum constants <em>of the type of the superclass</em>. The
 * query methods on the subclass will return all of the Enum constants from the
 * superclass and subclass.</p>
 *
 * <pre>
 * public final class ExtraColorEnum extends ColorEnum {
 *   // NOTE: Color enum declared above is final, change that to get this
 *   // example to compile.
 *   public static final ColorEnum YELLOW = new ExtraColorEnum("Yellow");
 *
 *   private ExtraColorEnum(String color) {
 *     super(color);
 *   }
 * 
 *   public static ColorEnum getEnum(String color) {
 *     return (ColorEnum) getEnum(ExtraColorEnum.class, color);
 *   }
 * 
 *   public static Map getEnumMap() {
 *     return getEnumMap(ExtraColorEnum.class);
 *   }
 * 
 *   public static List getEnumList() {
 *     return getEnumList(ExtraColorEnum.class);
 *   }
 * 
 *   public static Iterator iterator() {
 *     return iterator(ExtraColorEnum.class);
 *   }
 * }
 * </pre>
 *
 * <p>This example will return RED, GREEN, BLUE, YELLOW from the List and iterator
 * methods in that order. The RED, GREEN and BLUE instances will be the same (==) 
 * as those from the superclass ColorEnum. Note that YELLOW is declared as a
 * ColorEnum and not an ExtraColorEnum.</p>
 * 
 * <h4>Functional Enums</h4>
 *
 * <p>The enums can have functionality by defining subclasses and
 * overriding the <code>getEnumClass()</code> method:</p>
 * 
 * <pre>
 *   public static final OperationEnum PLUS = new PlusOperation();
 *   private static final class PlusOperation extends OperationEnum {
 *     private PlusOperation() {
 *       super("Plus");
 *     }
 *     public int eval(int a, int b) {
 *       return (a + b);
 *     }
 *   }
 *   public static final OperationEnum MINUS = new MinusOperation();
 *   private static final class MinusOperation extends OperationEnum {
 *     private MinusOperation() {
 *       super("Minus");
 *     }
 *     public int eval(int a, int b) {
 *       return (a - b);
 *     }
 *   }
 *
 *   private OperationEnum(String color) {
 *     super(color);
 *   }
 * 
 *   public final Class getEnumClass() {     // NOTE: new method!
 *     return OperationEnum.class;
 *   }
 *
 *   public abstract double eval(double a, double b);
 * 
 *   public static OperationEnum getEnum(String name) {
 *     return (OperationEnum) getEnum(OperationEnum.class, name);
 *   }
 * 
 *   public static Map getEnumMap() {
 *     return getEnumMap(OperationEnum.class);
 *   }
 * 
 *   public static List getEnumList() {
 *     return getEnumList(OperationEnum.class);
 *   }
 * 
 *   public static Iterator iterator() {
 *     return iterator(OperationEnum.class);
 *   }
 * }
 * </pre>
 * <p>The code above will work on JDK 1.2. If JDK1.3 and later is used,
 * the subclasses may be defined as anonymous.</p>
 *
 * @author Apache Avalon project
 * @author Stephen Colebourne
 * @author Chris Webb
 * @author Mike Bowler
 * @since 1.0
 * @version $Id: Enum.java,v 1.21 2003/08/21 15:52:55 ggregory Exp $
 */
public abstract class Enum implements Comparable, Serializable {

    /** Lang version 1.0.1 serial compatability */
    private static final long serialVersionUID = -487045951170455942L;
    
    // After discussion, the default size for HashMaps is used, as the
    // sizing algorithm changes across the JDK versions
    /**
     * An empty <code>Map</code>, as JDK1.2 didn't have an empty map.
     */
    private static final Map EMPTY_MAP = Collections.unmodifiableMap(new HashMap(0));
    
    /**
     * <code>Map</code>, key of class name, value of <code>Entry</code>.
     */
    private static final Map cEnumClasses = new HashMap();
    
    /**
     * The string representation of the Enum.
     */
    private final String iName;
    
    /**
     * The hashcode representation of the Enum.
     */
    private transient final int iHashCode;
    
    /**
     * The toString representation of the Enum.
     * @since 2.0
     */
    protected transient String iToString = null;

    /**
     * <p>Enable the iterator to retain the source code order.</p>
     */
    private static class Entry {
        /**
         * Map of Enum name to Enum.
         */
        final Map map = new HashMap();
        /**
         * Map of Enum name to Enum.
         */
        final Map unmodifiableMap = Collections.unmodifiableMap(map);
        /**
         * List of Enums in source code order.
         */
        final List list = new ArrayList(25);
        /**
         * Map of Enum name to Enum.
         */
        final List unmodifiableList = Collections.unmodifiableList(list);

        /**
         * <p>Restrictive constructor.</p>
         */
        private Entry() {
        }
    }

    /**
     * <p>Constructor to add a new named item to the enumeration.</p>
     *
     * @param name  the name of the enum object,
     *  must not be empty or <code>null</code>
     * @throws IllegalArgumentException if the name is <code>null</code>
     *  or an empty string
     * @throws IllegalArgumentException if the getEnumClass() method returns
     *  a null or invalid Class
     */
    protected Enum(String name) {
        super();
        init(name);