| /* |
| * 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; |
| |
| 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 $Id$ |
| */ |
| 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() { |
| super(); |
| } |
| |
| // 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 { |
| /** |
| * Required for serialization support. Declare serialization compatibility with Commons Lang 1.0 |
| * |
| * @see java.io.Serializable |
| */ |
| private static final long serialVersionUID = 7092611880189329093L; |
| |
| /** |
| * Restricted constructor - singleton. |
| */ |
| Null() { |
| super(); |
| } |
| |
| /** |
| * <p>Ensure singleton.</p> |
| * |
| * @return the singleton value |
| */ |
| private Object readResolve() { |
| return ObjectUtils.NULL; |
| } |
| } |
| |
| } |
