Add description and tests about the perils of nested enums
bug 23374 git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/proper/lang/trunk@137717 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Stephen Colebourne
parent
55a8a1e34c
commit
cd7aa49c16
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@ -214,13 +214,60 @@ import org.apache.commons.lang.StringUtils;
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* </pre>
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* <p>The code above will work on JDK 1.2. If JDK1.3 and later is used,
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* the subclasses may be defined as anonymous.</p>
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*
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* <h4>Nested class Enums</h4>
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*
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* <p>Care must be taken with class loading when defining a static nested class
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* for enums. The static nested class can be loaded without the surrounding outer
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* class being loaded. This can result in an empty list/map/iterator being returned.
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* One solution is to define a static block that references the outer class where
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* the constants are defined. For example:</p>
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*
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* <pre>
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* public final class Outer {
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* public static final BWEnum BLACK = new BWEnum("Black");
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* public static final BWEnum WHITE = new BWEnum("White");
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*
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* // static nested enum class
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* public static final class BWEnum extends Enum {
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*
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* static {
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* // explicitly reference BWEnum class to force constants to load
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* Object obj = Outer.BLACK;
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* }
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*
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* // ... other methods omitted
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* }
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* }
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* </pre>
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*
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* <p>Although the above solves the problem, it is not recommended. The best solution
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* is to define the constants in the enum class, and hold references in the outer class:
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*
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* <pre>
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* public final class Outer {
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* public static final BWEnum BLACK = BWEnum.BLACK;
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* public static final BWEnum WHITE = BWEnum.WHITE;
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*
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* // static nested enum class
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* public static final class BWEnum extends Enum {
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* // only define constants in enum classes - private if desired
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* private static final BWEnum BLACK = new BWEnum("Black");
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* private static final BWEnum WHITE = new BWEnum("White");
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*
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* // ... other methods omitted
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* }
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* }
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* </pre>
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*
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* <p>For more details, see the 'Nested' test cases.
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*
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* @author Apache Avalon project
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* @author Stephen Colebourne
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* @author Chris Webb
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* @author Mike Bowler
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* @since 1.0
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* @version $Id: Enum.java,v 1.22 2003/09/07 14:32:34 psteitz Exp $
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* @version $Id: Enum.java,v 1.23 2003/11/29 15:03:54 scolebourne Exp $
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*/
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public abstract class Enum implements Comparable, Serializable {
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@ -53,6 +53,8 @@
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*/
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package org.apache.commons.lang.enum;
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import java.util.ArrayList;
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import java.util.HashMap;
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import java.util.Iterator;
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import java.util.List;
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import java.util.Map;
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@ -67,7 +69,7 @@ import org.apache.commons.lang.SerializationUtils;
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* Test cases for the {@link Enum} class.
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*
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* @author Stephen Colebourne
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* @version $Id: EnumTest.java,v 1.11 2003/08/18 02:22:27 bayard Exp $
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* @version $Id: EnumTest.java,v 1.12 2003/11/29 15:03:54 scolebourne Exp $
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*/
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public final class EnumTest extends TestCase {
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@ -132,7 +134,7 @@ public final class EnumTest extends TestCase {
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}
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public void testList() {
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List list = ColorEnum.getEnumList();
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List list = new ArrayList(ColorEnum.getEnumList());
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assertNotNull(list);
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@ -146,19 +148,17 @@ public final class EnumTest extends TestCase {
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}
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public void testMap() {
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Map map = ColorEnum.getEnumMap();
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Map map = new HashMap(ColorEnum.getEnumMap());
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assertNotNull(map);
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assertEquals( map.keySet().size(),
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ColorEnum.getEnumList().size());
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assertTrue(map.containsValue(ColorEnum.RED));
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assertTrue(map.containsValue(ColorEnum.GREEN));
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assertTrue(map.containsValue(ColorEnum.BLUE));
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assertSame(ColorEnum.RED, map.get("Red"));
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assertSame(ColorEnum.GREEN, map.get("Green"));
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assertSame(ColorEnum.BLUE, map.get("Blue"));
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assertEquals( map.keySet().size(),
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ColorEnum.getEnumList().size());
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}
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public void testGet() {
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@ -415,4 +415,54 @@ public final class EnumTest extends TestCase {
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assertSame(Extended3Enum.DELTA, map.get("Delta"));
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}
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//-----------------------------------------------------------------------
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public void testNested() {
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List list = new ArrayList(Nest.ColorEnum.getEnumList());
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assertEquals(3, list.size()); // all is well
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Iterator it = list.iterator();
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assertSame(Nest.ColorEnum.RED, it.next());
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assertSame(Nest.ColorEnum.GREEN, it.next());
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assertSame(Nest.ColorEnum.BLUE, it.next());
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// This nesting works because the enum constants are defined in the SAME
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// class as the getEnumList(). It just acts as a normal enum.
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}
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public void testNestedBroken() {
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List list = new ArrayList(NestBroken.ColorEnum.getEnumList());
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assertEquals(0, list.size()); // no enums!!!
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// this is BROKEN because the enum constants are defined in a DIFFERENT
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// class from getEnumList(). Once NestBroken class is referenced,
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// and thus class loaded with its enum constants, the getEnumList works:
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new NestBroken();
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list = new ArrayList(NestBroken.ColorEnum.getEnumList());
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assertEquals(3, list.size()); // all is well!!!
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Iterator it = list.iterator();
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assertSame(NestBroken.RED, it.next());
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assertSame(NestBroken.GREEN, it.next());
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assertSame(NestBroken.BLUE, it.next());
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}
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public void testNestedLinked() {
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List list = new ArrayList(NestLinked.ColorEnum.getEnumList());
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assertEquals(3, list.size()); // all is well
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Iterator it = list.iterator();
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assertSame(NestLinked.RED, it.next());
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assertSame(NestLinked.GREEN, it.next());
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assertSame(NestLinked.BLUE, it.next());
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// This nesting works because a static block in the enum class forces a
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// class load of the outer class which defines the enum constants.
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}
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public void testNestedReferenced() {
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List list = new ArrayList(NestReferenced.ColorEnum.getEnumList());
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assertEquals(3, list.size()); // all is well
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Iterator it = list.iterator();
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assertSame(NestReferenced.RED, it.next());
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assertSame(NestReferenced.GREEN, it.next());
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assertSame(NestReferenced.BLUE, it.next());
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// This nesting works because the enum constants are actually defined in
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// the SAME class as the getEnumList(). The references in the outer class
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// are just extra references.
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}
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}
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@ -0,0 +1,100 @@
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/* ====================================================================
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* The Apache Software License, Version 1.1
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*
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* Copyright (c) 2002-2003 The Apache Software Foundation. All rights
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* reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* 3. The end-user documentation included with the redistribution, if
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* any, must include the following acknowledgement:
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* "This product includes software developed by the
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* Apache Software Foundation (http://www.apache.org/)."
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* Alternately, this acknowledgement may appear in the software itself,
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* if and wherever such third-party acknowledgements normally appear.
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*
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* 4. The names "The Jakarta Project", "Commons", and "Apache Software
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* Foundation" must not be used to endorse or promote products derived
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* from this software without prior written permission. For written
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* permission, please contact apache@apache.org.
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*
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* 5. Products derived from this software may not be called "Apache"
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* nor may "Apache" appear in their names without prior written
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* permission of the Apache Software Foundation.
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*
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
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* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
|
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* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
|
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
|
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
|
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* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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* ====================================================================
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*
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* This software consists of voluntary contributions made by many
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* individuals on behalf of the Apache Software Foundation. For more
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* information on the Apache Software Foundation, please see
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* <http://www.apache.org/>.
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*/
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package org.apache.commons.lang.enum;
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import java.util.Iterator;
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import java.util.List;
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import java.util.Map;
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/**
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* Color enumeration demonstrating a normal simple nesting case.
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* All is well here as the nested enum class is really no different
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* to any other class.
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*
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* @author Stephen Colebourne
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* @version $Id: Nest.java,v 1.1 2003/11/29 15:03:54 scolebourne Exp $
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*/
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public final class Nest {
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public Nest() {
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super();
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}
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public static final class ColorEnum extends Enum {
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public static final ColorEnum RED = new ColorEnum("Red");
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public static final ColorEnum GREEN = new ColorEnum("Green");
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public static final ColorEnum BLUE = new ColorEnum("Blue");
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private ColorEnum(String color) {
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super(color);
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}
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public static ColorEnum getEnum(String color) {
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return (ColorEnum) getEnum(ColorEnum.class, color);
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}
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public static Map getEnumMap() {
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return getEnumMap(ColorEnum.class);
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}
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public static List getEnumList() {
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return getEnumList(ColorEnum.class);
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}
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public static Iterator iterator() {
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return iterator(ColorEnum.class);
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}
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}
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}
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@ -0,0 +1,104 @@
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/* ====================================================================
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* The Apache Software License, Version 1.1
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*
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* Copyright (c) 2002-2003 The Apache Software Foundation. All rights
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* reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
|
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
|
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* notice, this list of conditions and the following disclaimer.
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*
|
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* 2. Redistributions in binary form must reproduce the above copyright
|
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* notice, this list of conditions and the following disclaimer in
|
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* 3. The end-user documentation included with the redistribution, if
|
||||
* any, must include the following acknowledgement:
|
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* "This product includes software developed by the
|
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* 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.
|
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*
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* 4. The names "The Jakarta Project", "Commons", and "Apache Software
|
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* Foundation" must not be used to endorse or promote products derived
|
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* from this software without prior written permission. For written
|
||||
* permission, please contact apache@apache.org.
|
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*
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* 5. Products derived from this software may not be called "Apache"
|
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* nor may "Apache" appear in their names without prior written
|
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* permission of the Apache Software Foundation.
|
||||
*
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* 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
|
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* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
|
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* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
|
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
|
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
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* SUCH DAMAGE.
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* ====================================================================
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*
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* This software consists of voluntary contributions made by many
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* individuals on behalf of the Apache Software Foundation. For more
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* information on the Apache Software Foundation, please see
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* <http://www.apache.org/>.
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*/
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package org.apache.commons.lang.enum;
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import java.util.Iterator;
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import java.util.List;
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import java.util.Map;
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/**
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* Color enumeration which demonstrates how to break the enum system.
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* <p>
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* The class loader sees the two classes here as independent - the enum
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* class is nested, not an inner class. Calling getEnumList() on ColorEnum
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* will return an empty list, unless and until the NestBroken class is
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* referenced.
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*
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* @author Stephen Colebourne
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* @version $Id: NestBroken.java,v 1.1 2003/11/29 15:03:54 scolebourne Exp $
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*/
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public final class NestBroken {
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public static final ColorEnum RED = new ColorEnum("Red");
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public static final ColorEnum GREEN = new ColorEnum("Green");
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public static final ColorEnum BLUE = new ColorEnum("Blue");
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public NestBroken() {
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super();
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}
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public static final class ColorEnum extends Enum {
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private ColorEnum(String color) {
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super(color);
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}
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public static ColorEnum getEnum(String color) {
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return (ColorEnum) getEnum(ColorEnum.class, color);
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}
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public static Map getEnumMap() {
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return getEnumMap(ColorEnum.class);
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}
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public static List getEnumList() {
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return getEnumList(ColorEnum.class);
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}
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public static Iterator iterator() {
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return iterator(ColorEnum.class);
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}
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}
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}
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@ -0,0 +1,111 @@
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/* ====================================================================
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* The Apache Software License, Version 1.1
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*
|
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* 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 apache@apache.org.
|
||||
*
|
||||
* 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/>.
|
||||
*/
|
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package org.apache.commons.lang.enum;
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import java.util.Iterator;
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import java.util.List;
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import java.util.Map;
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/**
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* Color enumeration which demonstrates how to define the constants in a
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* different class to the Enum. The extra <code>static{}</code> block is
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* needed to ensure that the enum constants are created before the
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* static methods on the ColorEnum are used.
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* <p>
|
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* The class loader sees the two classes here as independent - the enum
|
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* class is nested, not an inner class. The static block thus forces the
|
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* class load of the outer class, which is needed to initialise the enums.
|
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*
|
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* @author Stephen Colebourne
|
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* @version $Id: NestLinked.java,v 1.1 2003/11/29 15:03:54 scolebourne Exp $
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*/
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public final class NestLinked {
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public static final ColorEnum RED = new ColorEnum("Red");
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public static final ColorEnum GREEN = new ColorEnum("Green");
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public static final ColorEnum BLUE = new ColorEnum("Blue");
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public NestLinked() {
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super();
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}
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public static final class ColorEnum extends Enum {
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static {
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// Explicitly reference the class where the enums are defined
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Object obj = NestLinked.RED;
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}
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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);
|
||||
}
|
||||
}
|
||||
}
|
||||
|
|
@ -0,0 +1,107 @@
|
|||
/* ====================================================================
|
||||
* 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 apache@apache.org.
|
||||
*
|
||||
* 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.util.Iterator;
|
||||
import java.util.List;
|
||||
import java.util.Map;
|
||||
|
||||
/**
|
||||
* Color enumeration which demonstrates how to provide a view of the constants
|
||||
* in a different class to the Enum. This technique is the safest, however it
|
||||
* is obviously inconvenient as it involves defining two sets of constants.
|
||||
* See NestedLinked for an alternative.
|
||||
*
|
||||
* @author Stephen Colebourne
|
||||
* @version $Id: NestReferenced.java,v 1.1 2003/11/29 15:03:54 scolebourne Exp $
|
||||
*/
|
||||
|
||||
public final class NestReferenced {
|
||||
|
||||
public static final ColorEnum RED = ColorEnum.RED;
|
||||
public static final ColorEnum GREEN = ColorEnum.GREEN;
|
||||
public static final ColorEnum BLUE = ColorEnum.BLUE;
|
||||
|
||||
public NestReferenced() {
|
||||
super();
|
||||
}
|
||||
|
||||
public static final class ColorEnum extends Enum {
|
||||
|
||||
// must be defined here, not just in outer class
|
||||
private static final ColorEnum RED = new ColorEnum("Red");
|
||||
private static final ColorEnum GREEN = new ColorEnum("Green");
|
||||
private 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);
|
||||
}
|
||||
}
|
||||
}
|
||||
Loading…
Reference in New Issue