org.apache.commons.lang.enums.ValuedEnum Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.lang.enums;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Iterator;
import java.util.List;
import org.apache.commons.lang.ClassUtils;
/**
* Abstract superclass for type-safe enums with integer values suitable
* for use in switch statements.
*
* NOTE:Due to the way in which Java ClassLoaders work, comparing
* Enum objects should always be done using the equals() method,
* not ==. The equals() method will try == first so
* in most cases the effect is the same.
*
* To use this class, it must be subclassed. For example:
*
*
* public final class JavaVersionEnum extends ValuedEnum {
* //standard enums for version of JVM
* public static final int JAVA1_0_VALUE = 100;
* public static final int JAVA1_1_VALUE = 110;
* public static final int JAVA1_2_VALUE = 120;
* public static final int JAVA1_3_VALUE = 130;
* public static final JavaVersionEnum JAVA1_0 = new JavaVersionEnum( "Java 1.0", JAVA1_0_VALUE );
* public static final JavaVersionEnum JAVA1_1 = new JavaVersionEnum( "Java 1.1", JAVA1_1_VALUE );
* public static final JavaVersionEnum JAVA1_2 = new JavaVersionEnum( "Java 1.2", JAVA1_2_VALUE );
* public static final JavaVersionEnum JAVA1_3 = new JavaVersionEnum( "Java 1.3", JAVA1_3_VALUE );
*
* private JavaVersionEnum(String name, int value) {
* super( name, value );
* }
*
* public static JavaVersionEnum getEnum(String javaVersion) {
* return (JavaVersionEnum) getEnum(JavaVersionEnum.class, javaVersion);
* }
*
* public static JavaVersionEnum getEnum(int javaVersion) {
* return (JavaVersionEnum) getEnum(JavaVersionEnum.class, javaVersion);
* }
*
* public static Map getEnumMap() {
* return getEnumMap(JavaVersionEnum.class);
* }
*
* public static List getEnumList() {
* return getEnumList(JavaVersionEnum.class);
* }
*
* public static Iterator iterator() {
* return iterator(JavaVersionEnum.class);
* }
* }
*
*
* NOTE:These are declared final, so compilers may
* inline the code. Ensure you recompile everything when using final.
*
* The above class could then be used as follows:
*
*
* public void doSomething(JavaVersionEnum ver) {
* switch (ver.getValue()) {
* case JAVA1_0_VALUE:
* // ...
* break;
* case JAVA1_1_VALUE:
* // ...
* break;
* //...
* }
* }
*
*
* As shown, each enum has a name and a value. These can be accessed using
* getName and getValue.
*
* NOTE: Because the switch is ultimately sitting on top of an
* int, the example above is not type-safe. That is, there is nothing that
* checks that JAVA1_0_VALUE is a legal constant for JavaVersionEnum.
*
* The getEnum and iterator 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.
*
* @author Apache Avalon project
* @author Stephen Colebourne
* @since 2.1 (class existed in enum package from v1.0)
* @version $Id: ValuedEnum.java 466275 2006-10-20 22:02:34Z bayard $
*/
public abstract class ValuedEnum extends Enum {
/**
* Required for serialization support.
*
* @see java.io.Serializable
*/
private static final long serialVersionUID = -7129650521543789085L;
/**
* The value contained in enum.
*/
private final int iValue;
/**
* Constructor for enum item.
*
* @param name the name of enum item
* @param value the value of enum item
*/
protected ValuedEnum(String name, int value) {
super(name);
iValue = value;
}
/**
* Gets an Enum object by class and value.
*
* This method loops through the list of Enum,
* thus if there are many Enums this will be
* slow.
*
* @param enumClass the class of the Enum to get
* @param value the value of the Enum to get
* @return the enum object, or null if the enum does not exist
* @throws IllegalArgumentException if the enum class is null
*/
protected static Enum getEnum(Class enumClass, int value) {
if (enumClass == null) {
throw new IllegalArgumentException("The Enum Class must not be null");
}
List list = Enum.getEnumList(enumClass);
for (Iterator it = list.iterator(); it.hasNext();) {
ValuedEnum enumeration = (ValuedEnum) it.next();
if (enumeration.getValue() == value) {
return enumeration;
}
}
return null;
}
/**
* Get value of enum item.
*
* @return the enum item's value.
*/
public final int getValue() {
return iValue;
}
/**
* Tests for order.
*
* The default ordering is numeric by value, but this
* can be overridden by subclasses.
*
* NOTE: From v2.2 the enums must be of the same type.
* If the parameter is in a different class loader than this instance,
* reflection is used to compare the values.
*
* @see java.lang.Comparable#compareTo(Object)
* @param other the other object to compare to
* @return -ve if this is less than the other object, +ve if greater than,
* 0 of equal
* @throws ClassCastException if other is not an Enum
* @throws NullPointerException if other is null
*/
public int compareTo(Object other) {
if (other == this) {
return 0;
}
if (other.getClass() != this.getClass()) {
if (other.getClass().getName().equals(this.getClass().getName())) {
return iValue - getValueInOtherClassLoader(other);
}
throw new ClassCastException(
"Different enum class '" + ClassUtils.getShortClassName(other.getClass()) + "'");
}
return iValue - ((ValuedEnum) other).iValue;
}
/**
* Use reflection to return an objects value.
*
* @param other the object to determine the value for
* @return the value
*/
private int getValueInOtherClassLoader(Object other) {
try {
Method mth = other.getClass().getMethod("getValue", null);
Integer value = (Integer) mth.invoke(other, null);
return value.intValue();
} catch (NoSuchMethodException e) {
// ignore - should never happen
} catch (IllegalAccessException e) {
// ignore - should never happen
} catch (InvocationTargetException e) {
// ignore - should never happen
}
throw new IllegalStateException("This should not happen");
}
/**
* Human readable description of this Enum item.
*
* @return String in the form type[name=value], for example:
* JavaVersion[Java 1.0=100]. Note that the package name is
* stripped from the type name.
*/
public String toString() {
if (iToString == null) {
String shortName = ClassUtils.getShortClassName(getEnumClass());
iToString = shortName + "[" + getName() + "=" + getValue() + "]";
}
return iToString;
}
}