/*
* 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.caudexorigo.lang;
import java.io.Serializable;
import org.caudexorigo.text.StringUtils;
/**
* <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 Daniel L. Rall
* @author Stephen Colebourne
* @author Gary Gregory
* @author Mario Winterer
* @author <a href="mailto:david@davidkarlsen.com">David J. M. Karlsen</a>
* @since 1.0
* @version $Id: ObjectUtils.java 594336 2007-11-12 22:54:02Z bayard $
*/
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;
}
StringBuilder buffer = new StringBuilder();
identityToString(buffer, object);
return buffer.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 throw a NullPointerException for either of the two parameters.
* </p>
*
* <pre>
* ObjectUtils.identityToString(buf, "") = buf.append("java.lang.String@1e23"
* ObjectUtils.identityToString(buf, Boolean.TRUE) = buf.append("java.lang.Boolean@7fa"
* ObjectUtils.identityToString(buf, Boolean.TRUE) = buf.append("java.lang.Boolean@7fa")
* </pre>
*
* @param buffer
* the buffer to append to
* @param object
* the object to create a toString for
* @since 2.4
*/
public static void identityToString(StringBuilder buffer, Object object)
{
if (object == null)
{
throw new NullPointerException("Cannot get the toString of a null identity");
}
buffer.append(object.getClass().getName()).append('@').append(Integer.toHexString(System.identityHashCode(object)));
}
/**
* <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
* @deprecated The design of this method is bad - see LANG-360. Instead, use identityToString(StringBuilder, Object).
*/
public static StringBuilder appendIdentityToString(StringBuilder buffer, Object object)
{
if (object == null)
{
return null;
}
if (buffer == null)
{
buffer = new StringBuilder();
}
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();
}
// Min/Max
// -----------------------------------------------------------------------
/**
* Null safe comparison of Comparables.
*
* @param c1
* the first comparable, may be null
* @param c2
* the second comparable, may be null
* @return <ul>
* <li>If both objects are non-null and unequal, the lesser object.
* <li>If both objects are non-null and equal, c1.
* <li>If one of the comparables is null, the non-null object.
* <li>If both the comparables are null, null is returned.
* </ul>
*/
public static Object min(Comparable c1, Comparable c2)
{
if (c1 != null && c2 != null)
{
return c1.compareTo(c2) < 1 ? c1 : c2;
}
else
{
return c1 != null ? c1 : c2;
}
}
/**
* Null safe comparison of Comparables.
*
* @param c1
* the first comparable, may be null
* @param c2
* the second comparable, may be null
* @return <ul>
* <li>If both objects are non-null and unequal, the greater object.
* <li>If both objects are non-null and equal, c1.
* <li>If one of the comparables is null, the non-null object.
* <li>If both the comparables are null, null is returned.
* </ul>
*/
public static Object max(Comparable c1, Comparable c2)
{
if (c1 != null && c2 != null)
{
return c1.compareTo(c2) >= 0 ? c1 : c2;
}
else
{
return c1 != null ? c1 : c2;
}
}
// 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;
}
}
}