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.adapter;
18
19 import java.io.Serializable;
20
21 import org.apache.commons.functor.Function;
22 import org.apache.commons.functor.UnaryFunction;
23
24 /**
25 * Adapts a
26 * {@link UnaryFunction UnaryFunction}
27 * to the
28 * {@link Function Function} interface
29 * using a constant unary argument.
30 * <p/>
31 * Note that although this class implements
32 * {@link Serializable}, a given instance will
33 * only be truly <code>Serializable</code> if the
34 * underlying objects are. Attempts to serialize
35 * an instance whose delegates are not
36 * <code>Serializable</code> will result in an exception.
37 *
38 * @param <T> the returned value type.
39 * @version $Revision: 1157604 $ $Date: 2011-08-14 21:29:42 +0200 (Sun, 14 Aug 2011) $
40 * @author Rodney Waldhoff
41 */
42 public final class BoundFunction<T> implements Function<T>, Serializable {
43 /**
44 * serialVersionUID declaration.
45 */
46 private static final long serialVersionUID = 8873081237760986490L;
47 /** The {@link UnaryFunction UnaryFunction} I'm wrapping. */
48 private final UnaryFunction<Object, ? extends T> function;
49 /** The argument to pass to {@code function}. */
50 private final Object arg;
51
52 /**
53 * Create a new BoundFunction instance.
54 * @param <A> the argument value type
55 * @param function the function to adapt
56 * @param arg the constant argument to use
57 */
58 @SuppressWarnings("unchecked")
59 public <A> BoundFunction(UnaryFunction<? super A, ? extends T> function, A arg) {
60 if (function == null) {
61 throw new IllegalArgumentException("UnaryFunction argument was null");
62 }
63 this.function = (UnaryFunction<Object, ? extends T>) function;
64 this.arg = arg;
65 }
66
67 /**
68 * {@inheritDoc}
69 */
70 public T evaluate() {
71 return function.evaluate(arg);
72 }
73
74 /**
75 * {@inheritDoc}
76 */
77 public boolean equals(Object that) {
78 return that == this || (that instanceof BoundFunction<?> && equals((BoundFunction<?>) that));
79 }
80
81 /**
82 * Learn whether another BoundFunction is equal to this.
83 * @param that BoundFunction to test
84 * @return boolean
85 */
86 public boolean equals(BoundFunction<?> that) {
87 if (that == null) {
88 return false;
89 }
90 if (!(that.function.equals(this.function))) {
91 return false;
92 }
93 return that.arg == this.arg || that.arg != null && that.arg.equals(this.arg);
94 }
95
96 /**
97 * {@inheritDoc}
98 */
99 public int hashCode() {
100 int result = "BoundFunction".hashCode();
101 result <<= 2;
102 result |= function.hashCode();
103 result <<= 2;
104 return arg == null ? result : result | arg.hashCode();
105 }
106
107 /**
108 * {@inheritDoc}
109 */
110 public String toString() {
111 return "BoundFunction<" + function.toString() + "(" + arg + ")>";
112 }
113
114 /**
115 * Adapt the given, possibly-<code>null</code>,
116 * {@link UnaryFunction UnaryFunction} to the
117 * {@link Function Function} interface by binding
118 * the specified <code>Object</code> as a constant
119 * argument.
120 * When the given <code>UnaryFunction</code> is <code>null</code>,
121 * returns <code>null</code>.
122 * @param <A> input type
123 * @param <T> result type
124 * @param function the possibly-<code>null</code>
125 * {@link UnaryFunction UnaryFunction} to adapt
126 * @param arg the object to bind as a constant argument
127 * @return a <code>BoundFunction</code> wrapping the given
128 * {@link UnaryFunction UnaryFunction}, or <code>null</code>
129 * if the given <code>UnaryFunction</code> is <code>null</code>
130 */
131 public static <A, T> BoundFunction<T> bind(UnaryFunction<? super A, ? extends T> function, A arg) {
132 return null == function ? null : new BoundFunction<T>(function, arg);
133 }
134
135 }