1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.functor.core;
18
19 import java.io.Serializable;
20
21 import org.apache.commons.functor.UnaryFunction;
22 import org.apache.commons.functor.UnaryPredicate;
23
24 /**
25 * {@link #evaluate Evaluates} to its input argument.
26 *
27 * {@link #test Tests} to the <code>boolean</code>
28 * value of the <code>Boolean</code>-valued parameter.
29 * The {@link #test} method throws an exception if
30 * the parameter isn't a non-<code>null</code>
31 * <code>Boolean</code>.
32 *
33 * @param <T> the returned value type.
34 * @version $Revision: 1345136 $ $Date: 2012-06-01 09:47:06 -0300 (Fri, 01 Jun 2012) $
35 */
36 public final class Identity<T> implements UnaryFunction<T, T>, UnaryPredicate<T>, Serializable {
37 // static attributes
38 // ------------------------------------------------------------------------
39 /**
40 * A generic {@code Identity<Object>} instance.
41 */
42 public static final Identity<Object> INSTANCE = new Identity<Object>();
43
44 /**
45 * serialVersionUID declaration.
46 */
47 private static final long serialVersionUID = 4145504259013789494L;
48
49 // constructor
50 // ------------------------------------------------------------------------
51
52 /**
53 * Create a new Identity.
54 */
55 public Identity() {
56 }
57
58 // function interface
59 // ------------------------------------------------------------------------
60
61 /**
62 * {@inheritDoc}
63 */
64 public T evaluate(T obj) {
65 return obj;
66 }
67
68 /**
69 * {@inheritDoc}
70 */
71 public boolean test(Object obj) {
72 return test((Boolean) obj);
73 }
74
75 /**
76 * Test a Boolean object by returning its <code>booleanValue</code>.
77 * @param bool Boolean
78 * @return boolean
79 */
80 public boolean test(Boolean bool) {
81 return bool.booleanValue();
82 }
83
84 /**
85 * {@inheritDoc}
86 */
87 @Override
88 public boolean equals(Object that) {
89 return (that instanceof Identity<?>);
90 }
91
92 /**
93 * {@inheritDoc}
94 */
95 @Override
96 public int hashCode() {
97 return "Identity".hashCode();
98 }
99
100 /**
101 * {@inheritDoc}
102 */
103 @Override
104 public String toString() {
105 return "Identity";
106 }
107
108 // static methods
109 // ------------------------------------------------------------------------
110
111 /**
112 * Get an Identity instance.
113 * @param <T> the identity returned value type.
114 * @return Identity
115 */
116 public static <T> Identity<T> instance() {
117 return new Identity<T>();
118 }
119
120 }