/*
* Copyright 2002-2004 The Apache Software Foundation.
*
* Licensed 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;
import java.io.Serializable;
/**
* <p>Operations on <code>Object</code>.</p>
*
* <p>This class tries to handle <code>null</code> input gracefully.
* An exception will generally not be thrown for a <code>null</code> input.
* Each method documents its behaviour in more detail.</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
* @author Gary Gregory
* @author Mario Winterer
* @since 1.0
* @version $Id: ObjectUtils.java,v 1.24 2004/06/01 21:08:48 scolebourne 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() {
}
// Defaulting
//-----------------------------------------------------------------------
/**
* <p>Returns a default value if the object passed is
* <code>null</code>.</p>
*
* <pre>
* ObjectUtils.defaultIfNull(null, null) = null
* ObjectUtils.defaultIfNull(null, "") = ""
* ObjectUtils.defaultIfNull(null, "zz") = "zz"
* ObjectUtils.defaultIfNull("abc", *) = "abc"
* ObjectUtils.defaultIfNull(Boolean.TRUE, *) = Boolean.TRUE
* </pre>
*
* @param object the <code>Object</code> to test, may be <code>null</code>
* @param defaultValue the default value to return, may be <code>null</code>
* @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>
*
* <pre>
* ObjectUtils.equals(null, null) = true
* ObjectUtils.equals(null, "") = false
* ObjectUtils.equals("", null) = false
* ObjectUtils.equals("", "") = true
* ObjectUtils.equals(Boolean.TRUE, null) = false
* ObjectUtils.equals(Boolean.TRUE, "true") = false
* ObjectUtils.equals(Boolean.TRUE, Boolean.TRUE) = true
* ObjectUtils.equals(Boolean.TRUE, Boolean.FALSE) = false
* </pre>
*
* @param object1 the first object, may be <code>null</code>
* @param object2 the second object, may be <code>null</code>
* @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 hash code of an object returning zero when the
* object is <code>null</code>.</p>
*
* <pre>
* ObjectUtils.hashCode(null) = 0
* ObjectUtils.hashCode(obj) = obj.hashCode()
* </pre>
*
* @param obj the object to obtain the hash code of, may be <code>null</code>
* @return the hash code of the object, or zero if null
* @since 2.1
*/
public static int hashCode(Object obj) {
return ((obj == null) ? 0 : obj.hashCode());
}
// Identity ToString
//-----------------------------------------------------------------------
/**
* <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>
*
* <pre>
* ObjectUtils.identityToString(null) = null
* ObjectUtils.identityToString("") = "java.lang.String@1e23"
* ObjectUtils.identityToString(Boolean.TRUE) = "java.lang.Boolean@7fa"
* </pre>
*
* @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 appendIdentityToString(null, object).toString();
}
/**
* <p>Appends 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>
*
* <pre>
* ObjectUtils.appendIdentityToString(*, null) = null
* ObjectUtils.appendIdentityToString(null, "") = "java.lang.String@1e23"
* ObjectUtils.appendIdentityToString(null, Boolean.TRUE) = "java.lang.Boolean@7fa"
* ObjectUtils.appendIdentityToString(buf, Boolean.TRUE) = buf.append("java.lang.Boolean@7fa")
* </pre>
*
* @param buffer the buffer to append to, may be <code>null</code>
* @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
* @since 2.0
*/
public static StringBuffer appendIdentityToString(StringBuffer buffer, Object object) {
if (object == null) {
return null;
}
if (buffer == null) {
buffer = new StringBuffer();
}
return buffer
.append(object.getClass().getName())
.append('@')
.append(Integer.toHexString(System.identityHashCode(object)));
}
// ToString
//-----------------------------------------------------------------------
/**
* <p>Gets the <code>toString</code> of an <code>Object</code> returning
* an empty string ("") if <code>null</code> input.</p>
*
* <pre>
* ObjectUtils.toString(null) = ""
* ObjectUtils.toString("") = ""
* ObjectUtils.toString("bat") = "bat"
* ObjectUtils.toString(Boolean.TRUE) = "true"
* </pre>
*
* @see StringUtils#defaultString(String)
* @see String#valueOf(Object)
* @param obj the Object to <code>toString</code>, may be null
* @return the passed in Object's toString, or nullStr if <code>null</code> input
* @since 2.0
*/
public static String toString(Object obj) {
return (obj == null ? "" : obj.toString());
}
/**
* <p>Gets the <code>toString</code> of an <code>Object</code> returning
* a specified text if <code>null</code> input.</p>
*
* <pre>
* ObjectUtils.toString(null, null) = null
* ObjectUtils.toString(null, "null") = "null"
* ObjectUtils.toString("", "null") = ""
* ObjectUtils.toString("bat", "null") = "bat"
* ObjectUtils.toString(Boolean.TRUE, "null") = "true"
* </pre>
*
* @see StringUtils#defaultString(String,String)
* @see String#valueOf(Object)
* @param obj the Object to <code>toString</code>, may be null
* @param nullStr the String to return if <code>null</code> input, may be null
* @return the passed in Object's toString, or nullStr if <code>null</code> input
* @since 2.0
*/
public static String toString(Object obj, String nullStr) {
return (obj == null ? nullStr : obj.toString());
}
// Null
//-----------------------------------------------------------------------
/**
* <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 compatibility 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;
}
}
}
