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.adapter;
018
019 import java.io.Serializable;
020
021 import org.apache.commons.functor.Function;
022 import org.apache.commons.functor.UnaryFunction;
023
024 /**
025 * Adapts a
026 * {@link UnaryFunction UnaryFunction}
027 * to the
028 * {@link Function Function} interface
029 * using a constant unary argument.
030 * <p/>
031 * Note that although this class implements
032 * {@link Serializable}, a given instance will
033 * only be truly <code>Serializable</code> if the
034 * underlying objects are. Attempts to serialize
035 * an instance whose delegates are not
036 * <code>Serializable</code> will result in an exception.
037 *
038 * @param <T> the returned value type.
039 * @version $Revision: 1157604 $ $Date: 2011-08-14 21:29:42 +0200 (Sun, 14 Aug 2011) $
040 * @author Rodney Waldhoff
041 */
042 public final class BoundFunction<T> implements Function<T>, Serializable {
043 /**
044 * serialVersionUID declaration.
045 */
046 private static final long serialVersionUID = 8873081237760986490L;
047 /** The {@link UnaryFunction UnaryFunction} I'm wrapping. */
048 private final UnaryFunction<Object, ? extends T> function;
049 /** The argument to pass to {@code function}. */
050 private final Object arg;
051
052 /**
053 * Create a new BoundFunction instance.
054 * @param <A> the argument value type
055 * @param function the function to adapt
056 * @param arg the constant argument to use
057 */
058 @SuppressWarnings("unchecked")
059 public <A> BoundFunction(UnaryFunction<? super A, ? extends T> function, A arg) {
060 if (function == null) {
061 throw new IllegalArgumentException("UnaryFunction argument was null");
062 }
063 this.function = (UnaryFunction<Object, ? extends T>) function;
064 this.arg = arg;
065 }
066
067 /**
068 * {@inheritDoc}
069 */
070 public T evaluate() {
071 return function.evaluate(arg);
072 }
073
074 /**
075 * {@inheritDoc}
076 */
077 public boolean equals(Object that) {
078 return that == this || (that instanceof BoundFunction<?> && equals((BoundFunction<?>) that));
079 }
080
081 /**
082 * Learn whether another BoundFunction is equal to this.
083 * @param that BoundFunction to test
084 * @return boolean
085 */
086 public boolean equals(BoundFunction<?> that) {
087 if (that == null) {
088 return false;
089 }
090 if (!(that.function.equals(this.function))) {
091 return false;
092 }
093 return that.arg == this.arg || that.arg != null && that.arg.equals(this.arg);
094 }
095
096 /**
097 * {@inheritDoc}
098 */
099 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 }