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.composite;
018
019 import java.io.Serializable;
020
021 import org.apache.commons.functor.Function;
022 import org.apache.commons.functor.Predicate;
023
024 /**
025 * A {@link Function Function}
026 * similiar to Java's "ternary"
027 * or "conditional" operator (<code>? :</code>).
028 * Given a {@link Predicate predicate}
029 * <i>p</i> and {@link Function functions}
030 * <i>f</i> and <i>g</i>, {@link #evaluate evaluates}
031 * to
032 * <code>p.test() ? f.evaluate() : g.evaluate()</code>.
033 * <p>
034 * Note that although this class implements
035 * {@link Serializable}, a given instance will
036 * only be truly <code>Serializable</code> if all the
037 * underlying functors are. Attempts to serialize
038 * an instance whose delegates are not all
039 * <code>Serializable</code> will result in an exception.
040 * </p>
041 * @version $Revision: 1166386 $ $Date: 2011-09-07 22:28:01 +0200 (Wed, 07 Sep 2011) $
042 * @author Rodney Waldhoff
043 */
044 public final class ConditionalFunction<T> implements Function<T>, Serializable {
045 /**
046 * serialVersionUID declaration.
047 */
048 private static final long serialVersionUID = 4214871352184887792L;
049
050 /** Base hash integer used to shift hash */
051 private static final int HASH_SHIFT = 4;
052 // attributes
053 // ------------------------------------------------------------------------
054 private final Predicate ifPred;
055 private final Function<? extends T> thenFunc;
056 private final Function<? extends T> elseFunc;
057
058 // constructor
059 // ------------------------------------------------------------------------
060 /**
061 * Create a new ConditionalFunction.
062 * @param ifPred if
063 * @param thenFunc then
064 * @param elseFunc else
065 */
066 public ConditionalFunction(Predicate ifPred, Function<? extends T> thenFunc, Function<? extends T> elseFunc) {
067 if (ifPred == null) {
068 throw new IllegalArgumentException("Predicate argument was null");
069 }
070 this.ifPred = ifPred;
071 if (thenFunc == null || elseFunc == null) {
072 throw new IllegalArgumentException("One or more Function arguments was null");
073 }
074 this.thenFunc = thenFunc;
075 this.elseFunc = elseFunc;
076 }
077
078 // predicate interface
079 // ------------------------------------------------------------------------
080 /**
081 * {@inheritDoc}
082 */
083 public T evaluate() {
084 if (ifPred.test()) {
085 return thenFunc.evaluate();
086 } else {
087 return elseFunc.evaluate();
088 }
089 }
090
091 /**
092 * {@inheritDoc}
093 */
094 public boolean equals(Object that) {
095 return that == this || (that instanceof ConditionalFunction<?> && equals((ConditionalFunction<?>) that));
096 }
097
098 /**
099 * Learn whether another ConditionalFunction is equal to this.
100 * @param that ConditionalFunction to test
101 * @return boolean
102 */
103 public boolean equals(ConditionalFunction<?> that) {
104 return null != that
105 && (null == ifPred ? null == that.ifPred : ifPred.equals(that.ifPred))
106 && (null == thenFunc ? null == that.thenFunc : thenFunc.equals(that.thenFunc))
107 && (null == elseFunc ? null == that.elseFunc : elseFunc.equals(that.elseFunc));
108 }
109
110 /**
111 * {@inheritDoc}
112 */
113 public int hashCode() {
114 int hash = "ConditionalFunction".hashCode();
115 if (null != ifPred) {
116 hash <<= HASH_SHIFT;
117 hash ^= ifPred.hashCode();
118 }
119 if (null != thenFunc) {
120 hash <<= HASH_SHIFT;
121 hash ^= thenFunc.hashCode();
122 }
123 if (null != elseFunc) {
124 hash <<= HASH_SHIFT;
125 hash ^= elseFunc.hashCode();
126 }
127 return hash;
128 }
129
130 /**
131 * {@inheritDoc}
132 */
133 public String toString() {
134 return "ConditionalFunction<" + ifPred + "?" + thenFunc + ":" + elseFunc + ">";
135 }
136
137 }