    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    }