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.BinaryFunction;
22 import org.apache.commons.functor.UnaryFunction;
23
24 /**
25 * Adapts a
26 * {@link BinaryFunction BinaryFunction}
27 * to the
28 * {@link UnaryFunction UnaryFunction} interface
29 * using a constant left-side 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 <A> the argument type.
39 * @param <T> the returned value type.
40 * @version $Revision: 1157618 $ $Date: 2011-08-14 21:54:43 +0200 (Sun, 14 Aug 2011) $
41 * @author Rodney Waldhoff
42 */
43 public final class LeftBoundFunction<A, T> implements UnaryFunction<A, T>, Serializable {
44 /**
45 * serialVersionUID declaration.
46 */
47 private static final long serialVersionUID = -7456827102718911769L;
48 /** The {@link BinaryFunction BinaryFunction} I'm wrapping. */
49 private final BinaryFunction<Object, ? super A, ? extends T> function;
50 /** The parameter to pass to {@code function}. */
51 private final Object param;
52
53 /**
54 * Create a new LeftBoundFunction instance.
55 * @param <L> bound arg type
56 * @param function the function to adapt
57 * @param arg the constant argument to use
58 */
59 @SuppressWarnings("unchecked")
60 public <L> LeftBoundFunction(BinaryFunction<? super L, ? super A, ? extends T> function, L arg) {
61 if (function == null) {
62 throw new IllegalArgumentException("BinaryFunction argument was null");
63 }
64 this.function = (BinaryFunction<Object, ? super A, ? extends T>) function;
65 this.param = arg;
66 }
67
68 /**
69 * {@inheritDoc}
70 */
71 public T evaluate(A obj) {
72 return function.evaluate(param, obj);
73 }
74
75 /**
76 * {@inheritDoc}
77 */
78 public boolean equals(Object that) {
79 return that == this || (that instanceof LeftBoundFunction<?, ?> && equals((LeftBoundFunction<?, ?>) that));
80 }
81
82 /**
83 * Learn whether another LeftBoundFunction is equal to this.
84 * @param that LeftBoundFunction to test
85 * @return boolean
86 */
87 public boolean equals(LeftBoundFunction<?, ?> that) {
88 return null != that
89 && (null == function ? null == that.function : function.equals(that.function))
90 && (null == param ? null == that.param : param.equals(that.param));
91 }
92
93 /**
94 * {@inheritDoc}
95 */
96 public int hashCode() {
97 int hash = "LeftBoundFunction".hashCode();
98 if (null != function) {
99 hash <<= 2;
100 hash ^= function.hashCode();
101 }
102 if (null != param) {
103 hash <<= 2;
104 hash ^= param.hashCode();
105 }
106 return hash;
107 }
108
109 /**
110 * {@inheritDoc}
111 */
112 public String toString() {
113 return "LeftBoundFunction<" + function + "(" + param + ",?)>";
114 }
115
116 /**
117 * Adapt a BinaryFunction as a UnaryFunction.
118 * @param <L> left type
119 * @param <R> right type
120 * @param <T> result type
121 * @param function to adapt
122 * @param arg left side argument
123 * @return LeftBoundFunction
124 */
125 public static <L, R, T> LeftBoundFunction<R, T> bind(
126 BinaryFunction<? super L, ? super R, ? extends T> function, L arg) {
127 return null == function ? null : new LeftBoundFunction<R, T>(function, arg);
128 }
129
130 }