| /* ==================================================================== |
| * 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 acknowlegement: |
| * "This product includes software developed by the |
| * Apache Software Foundation (http://www.apache.org/)." |
| * Alternately, this acknowlegement may appear in the software itself, |
| * if and wherever such third-party acknowlegements 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; |
| |
| import java.io.Serializable; |
| /** |
| * <p>Common <code>Object</code> manipulation routines.</p> |
| * |
| * @author <a href="mailto:nissim@nksystems.com">Nissim Karpenstein</a> |
| * @author <a href="mailto:janekdb@yahoo.co.uk">Janek Bogucki</a> |
| * @author <a href="mailto:dlr@finemaltcoding.com">Daniel Rall</a> |
| * @author Stephen Colebourne |
| * @since 1.0 |
| * @version $Id: ObjectUtils.java,v 1.9 2003/07/14 22:25:03 bayard Exp $ |
| */ |
| public class ObjectUtils { |
| |
| /** |
| * <p>Singleton used as a <code>null</code> placeholder where |
| * <code>null</code> has another meaning.</p> |
| * |
| * <p>For example, in a <code>HashMap</code> the |
| * {@link java.util.HashMap#get(java.lang.Object)} method returns |
| * <code>null</code> if the <code>Map</code> contains |
| * <code>null</code> or if there is no matching key. The |
| * <code>Null</code> placeholder can be used to distinguish between |
| * these two cases.</p> |
| * |
| * <p>Another example is <code>Hashtable</code>, where <code>null</code> |
| * cannot be stored.</p> |
| * |
| * <p>This instance is Serializable.</p> |
| */ |
| public static final Null NULL = new Null(); |
| |
| /** |
| * <p><code>ObjectUtils</code> instances should NOT be constructed in |
| * standard programming. Instead, the class should be used as |
| * <code>ObjectUtils.defaultIfNull("a","b");</code>.</p> |
| * |
| * <p>This constructor is public to permit tools that require a JavaBean instance |
| * to operate.</p> |
| */ |
| public ObjectUtils() { |
| } |
| |
| //-------------------------------------------------------------------- |
| |
| /** |
| * <p>Returns a default value if the object passed is |
| * <code>null</code>.</p> |
| * |
| * @param object the <code>Object</code> to test |
| * @param defaultValue the default value to return |
| * @return <code>object</code> if it is not <code>null</code>, defaultValue otherwise |
| */ |
| public static Object defaultIfNull(Object object, Object defaultValue) { |
| return (object != null ? object : defaultValue); |
| } |
| |
| /** |
| * <p>Compares two objects for equality, where either one or both |
| * objects may be <code>null</code>.</p> |
| * |
| * @param object1 the first object |
| * @param object2 the second object |
| * @return <code>true</code> if the values of both objects are the same |
| */ |
| public static boolean equals(Object object1, Object object2) { |
| if (object1 == object2) { |
| return true; |
| } |
| if ((object1 == null) || (object2 == null)) { |
| return false; |
| } |
| return object1.equals(object2); |
| } |
| |
| /** |
| * <p>Gets the toString that would be produced by <code>Object</code> |
| * if a class did not override toString itself. <code>Null</code> |
| * will return <code>null</code>.</p> |
| * |
| * @param object the object to create a toString for, may be |
| * <code>null</code> |
| * @return the default toString text, or <code>null</code> if |
| * <code>null</code> passed in |
| */ |
| public static String identityToString(Object object) { |
| if (object == null) { |
| return null; |
| } |
| return new StringBuffer() |
| .append(object.getClass().getName()) |
| .append('@') |
| .append(Integer.toHexString(System.identityHashCode(object))) |
| .toString(); |
| } |
| |
| /** |
| * <p>Class used as a null placeholder where <code>null</code> |
| * has another meaning.</p> |
| * |
| * <p>For example, in a <code>HashMap</code> the |
| * {@link java.util.HashMap#get(java.lang.Object)} method returns |
| * <code>null</code> if the <code>Map</code> contains |
| * <code>null</code> or if there is no matching key. The |
| * <code>Null</code> placeholder can be used to distinguish between |
| * these two cases.</p> |
| * |
| * <p>Another example is <code>Hashtable</code>, where <code>null</code> |
| * cannot be stored.</p> |
| */ |
| public static class Null implements Serializable { |
| // declare serialization compatability with Commons Lang 1.0 |
| private static final long serialVersionUID = 7092611880189329093L; |
| |
| /** |
| * Restricted constructor - singleton. |
| */ |
| Null() { |
| } |
| |
| /** |
| * <p>Ensure singleton.</p> |
| * |
| * @return the singleton value |
| */ |
| private Object readResolve() { |
| return ObjectUtils.NULL; |
| } |
| } |
| |
| } |
