001 /*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017 package org.apache.commons.functor.core;
018
019 import java.io.Serializable;
020
021 import org.apache.commons.functor.UnaryFunction;
022 import org.apache.commons.functor.UnaryPredicate;
023
024 /**
025 * {@link #evaluate Evaluates} to its input argument.
026 *
027 * {@link #test Tests} to the <code>boolean</code>
028 * value of the <code>Boolean</code>-valued parameter.
029 * The {@link #test} method throws an exception if
030 * the parameter isn't a non-<code>null</code>
031 * <code>Boolean</code>.
032 *
033 * @param <T> the returned value type.
034 * @version $Revision: 1160385 $ $Date: 2011-08-22 21:28:37 +0200 (Mon, 22 Aug 2011) $
035 * @author Rodney Waldhoff
036 */
037 public final class Identity<T> implements UnaryFunction<T, T>, UnaryPredicate<T>, Serializable {
038 // static attributes
039 // ------------------------------------------------------------------------
040 /**
041 * A generic {@code Identity<Object>} instance.
042 */
043 public static final Identity<Object> INSTANCE = new Identity<Object>();
044
045 /**
046 * serialVersionUID declaration.
047 */
048 private static final long serialVersionUID = 4145504259013789494L;
049
050 // constructor
051 // ------------------------------------------------------------------------
052
053 /**
054 * Create a new Identity.
055 */
056 public Identity() {
057 }
058
059 // function interface
060 // ------------------------------------------------------------------------
061
062 /**
063 * {@inheritDoc}
064 */
065 public T evaluate(T obj) {
066 return obj;
067 }
068
069 /**
070 * {@inheritDoc}
071 */
072 public boolean test(Object obj) {
073 return test((Boolean) obj);
074 }
075
076 /**
077 * Test a Boolean object by returning its <code>booleanValue</code>.
078 * @param bool Boolean
079 * @return boolean
080 */
081 public boolean test(Boolean bool) {
082 return bool.booleanValue();
083 }
084
085 /**
086 * {@inheritDoc}
087 */
088 public boolean equals(Object that) {
089 return (that instanceof Identity<?>);
090 }
091
092 /**
093 * {@inheritDoc}
094 */
095 public int hashCode() {
096 return "Identity".hashCode();
097 }
098
099 /**
100 * {@inheritDoc}
101 */
102 public String toString() {
103 return "Identity";
104 }
105
106 // static methods
107 // ------------------------------------------------------------------------
108
109 /**
110 * Get an Identity instance.
111 * @param <T> the identity returned value type.
112 * @return Identity
113 */
114 public static <T> Identity<T> instance() {
115 return new Identity<T>();
116 }
117
118 }