001 /*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017 package org.apache.commons.lang.enums;
018
019 import java.lang.reflect.InvocationTargetException;
020 import java.lang.reflect.Method;
021 import java.util.Iterator;
022 import java.util.List;
023
024 import org.apache.commons.lang.ClassUtils;
025
026 /**
027 * <p>Abstract superclass for type-safe enums with integer values suitable
028 * for use in <code>switch</code> statements.</p>
029 *
030 * <p><em>NOTE:</em>Due to the way in which Java ClassLoaders work, comparing
031 * <code>Enum</code> objects should always be done using the equals() method,
032 * not <code>==</code>. The equals() method will try <code>==</code> first so
033 * in most cases the effect is the same.</p>
034 *
035 * <p>To use this class, it must be subclassed. For example:</p>
036 *
037 * <pre>
038 * public final class JavaVersionEnum extends ValuedEnum {
039 * //standard enums for version of JVM
040 * public static final int JAVA1_0_VALUE = 100;
041 * public static final int JAVA1_1_VALUE = 110;
042 * public static final int JAVA1_2_VALUE = 120;
043 * public static final int JAVA1_3_VALUE = 130;
044 * public static final JavaVersionEnum JAVA1_0 = new JavaVersionEnum( "Java 1.0", JAVA1_0_VALUE );
045 * public static final JavaVersionEnum JAVA1_1 = new JavaVersionEnum( "Java 1.1", JAVA1_1_VALUE );
046 * public static final JavaVersionEnum JAVA1_2 = new JavaVersionEnum( "Java 1.2", JAVA1_2_VALUE );
047 * public static final JavaVersionEnum JAVA1_3 = new JavaVersionEnum( "Java 1.3", JAVA1_3_VALUE );
048 *
049 * private JavaVersionEnum(String name, int value) {
050 * super( name, value );
051 * }
052 *
053 * public static JavaVersionEnum getEnum(String javaVersion) {
054 * return (JavaVersionEnum) getEnum(JavaVersionEnum.class, javaVersion);
055 * }
056 *
057 * public static JavaVersionEnum getEnum(int javaVersion) {
058 * return (JavaVersionEnum) getEnum(JavaVersionEnum.class, javaVersion);
059 * }
060 *
061 * public static Map getEnumMap() {
062 * return getEnumMap(JavaVersionEnum.class);
063 * }
064 *
065 * public static List getEnumList() {
066 * return getEnumList(JavaVersionEnum.class);
067 * }
068 *
069 * public static Iterator iterator() {
070 * return iterator(JavaVersionEnum.class);
071 * }
072 * }
073 * </pre>
074 *
075 * <p><em>NOTE:</em>These are declared <code>final</code>, so compilers may
076 * inline the code. Ensure you recompile everything when using final. </p>
077 *
078 * <p>The above class could then be used as follows:</p>
079 *
080 * <pre>
081 * public void doSomething(JavaVersionEnum ver) {
082 * switch (ver.getValue()) {
083 * case JAVA1_0_VALUE:
084 * // ...
085 * break;
086 * case JAVA1_1_VALUE:
087 * // ...
088 * break;
089 * //...
090 * }
091 * }
092 * </pre>
093 *
094 * <p>As shown, each enum has a name and a value. These can be accessed using
095 * <code>getName</code> and <code>getValue</code>.</p>
096 *
097 * <p><em>NOTE:</em> Because the switch is ultimately sitting on top of an
098 * int, the example above is not type-safe. That is, there is nothing that
099 * checks that JAVA1_0_VALUE is a legal constant for JavaVersionEnum. </p>
100 *
101 * <p>The <code>getEnum</code> and <code>iterator</code> methods are recommended.
102 * Unfortunately, Java restrictions require these to be coded as shown in each subclass.
103 * An alternative choice is to use the {@link EnumUtils} class.</p>
104 *
105 * @author Apache Avalon project
106 * @author Apache Software Foundation
107 * @since 2.1 (class existed in enum package from v1.0)
108 * @version $Id: ValuedEnum.java 905636 2010-02-02 14:03:32Z niallp $
109 */
110 public abstract class ValuedEnum extends Enum {
111
112 /**
113 * Required for serialization support.
114 *
115 * @see java.io.Serializable
116 */
117 private static final long serialVersionUID = -7129650521543789085L;
118
119 /**
120 * The value contained in enum.
121 */
122 private final int iValue;
123
124 /**
125 * Constructor for enum item.
126 *
127 * @param name the name of enum item
128 * @param value the value of enum item
129 */
130 protected ValuedEnum(String name, int value) {
131 super(name);
132 iValue = value;
133 }
134
135 /**
136 * <p>Gets an <code>Enum</code> object by class and value.</p>
137 *
138 * <p>This method loops through the list of <code>Enum</code>,
139 * thus if there are many <code>Enum</code>s this will be
140 * slow.</p>
141 *
142 * @param enumClass the class of the <code>Enum</code> to get
143 * @param value the value of the <code>Enum</code> to get
144 * @return the enum object, or null if the enum does not exist
145 * @throws IllegalArgumentException if the enum class is <code>null</code>
146 */
147 protected static Enum getEnum(Class enumClass, int value) {
148 if (enumClass == null) {
149 throw new IllegalArgumentException("The Enum Class must not be null");
150 }
151 List list = Enum.getEnumList(enumClass);
152 for (Iterator it = list.iterator(); it.hasNext();) {
153 ValuedEnum enumeration = (ValuedEnum) it.next();
154 if (enumeration.getValue() == value) {
155 return enumeration;
156 }
157 }
158 return null;
159 }
160
161 /**
162 * <p>Get value of enum item.</p>
163 *
164 * @return the enum item's value.
165 */
166 public final int getValue() {
167 return iValue;
168 }
169
170 /**
171 * <p>Tests for order.</p>
172 *
173 * <p>The default ordering is numeric by value, but this
174 * can be overridden by subclasses.</p>
175 *
176 * <p>NOTE: From v2.2 the enums must be of the same type.
177 * If the parameter is in a different class loader than this instance,
178 * reflection is used to compare the values.</p>
179 *
180 * @see java.lang.Comparable#compareTo(Object)
181 * @param other the other object to compare to
182 * @return -ve if this is less than the other object, +ve if greater than,
183 * <code>0</code> of equal
184 * @throws ClassCastException if other is not an <code>Enum</code>
185 * @throws NullPointerException if other is <code>null</code>
186 */
187 public int compareTo(Object other) {
188 if (other == this) {
189 return 0;
190 }
191 if (other.getClass() != this.getClass()) {
192 if (other.getClass().getName().equals(this.getClass().getName())) {
193 return iValue - getValueInOtherClassLoader(other);
194 }
195 throw new ClassCastException(
196 "Different enum class '" + ClassUtils.getShortClassName(other.getClass()) + "'");
197 }
198 return iValue - ((ValuedEnum) other).iValue;
199 }
200
201 /**
202 * <p>Use reflection to return an objects value.</p>
203 *
204 * @param other the object to determine the value for
205 * @return the value
206 */
207 private int getValueInOtherClassLoader(Object other) {
208 try {
209 Method mth = other.getClass().getMethod("getValue", null);
210 Integer value = (Integer) mth.invoke(other, null);
211 return value.intValue();
212 } catch (NoSuchMethodException e) {
213 // ignore - should never happen
214 } catch (IllegalAccessException e) {
215 // ignore - should never happen
216 } catch (InvocationTargetException e) {
217 // ignore - should never happen
218 }
219 throw new IllegalStateException("This should not happen");
220 }
221
222 /**
223 * <p>Human readable description of this <code>Enum</code> item.</p>
224 *
225 * @return String in the form <code>type[name=value]</code>, for example:
226 * <code>JavaVersion[Java 1.0=100]</code>. Note that the package name is
227 * stripped from the type name.
228 */
229 public String toString() {
230 if (iToString == null) {
231 String shortName = ClassUtils.getShortClassName(getEnumClass());
232 iToString = shortName + "[" + getName() + "=" + getValue() + "]";
233 }
234 return iToString;
235 }
236 }