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.BinaryPredicate;
22 import org.apache.commons.functor.UnaryPredicate;
23 import org.apache.commons.functor.adapter.IgnoreLeftPredicate;
24 import org.apache.commons.functor.adapter.IgnoreRightPredicate;
25
26 /**
27 * {@link #test Tests}
28 * <code>true</code> iff its argument
29 * is <code>null</code>.
30 *
31 * @param <A> the argument type.
32 * @version $Revision: 1160407 $ $Date: 2011-08-22 22:03:21 +0200 (Mon, 22 Aug 2011) $
33 * @author Rodney Waldhoff
34 */
35 public final class IsNull<A> implements UnaryPredicate<A>, Serializable {
36
37 // static attributes
38 // ------------------------------------------------------------------------
39 /**
40 * Basic IsNull instance.
41 */
42 public static final IsNull<Object> INSTANCE = IsNull.<Object>instance();
43
44 /**
45 * Left-handed BinaryPredicate.
46 */
47 public static final BinaryPredicate<Object, Object> LEFT = IsNull.<Object>left();
48
49 /**
50 * Right-handed BinaryPredicate.
51 */
52 public static final BinaryPredicate<Object, Object> RIGHT = IsNull.<Object>right();
53
54 /**
55 * serialVersionUID declaration.
56 */
57 private static final long serialVersionUID = 6001380107746171952L;
58
59 // constructor
60 // ------------------------------------------------------------------------
61 /**
62 * Create a new IsNull.
63 */
64 public IsNull() {
65 }
66
67 // predicate interface
68 // ------------------------------------------------------------------------
69 /**
70 * {@inheritDoc}
71 */
72 public boolean test(A obj) {
73 return (null == obj);
74 }
75
76 /**
77 * {@inheritDoc}
78 */
79 public boolean equals(Object that) {
80 return that instanceof IsNull<?>;
81 }
82
83 /**
84 * {@inheritDoc}
85 */
86 public int hashCode() {
87 return "IsNull".hashCode();
88 }
89
90 /**
91 * {@inheritDoc}
92 */
93 public String toString() {
94 return "IsNull";
95 }
96
97 // static methods
98 // ------------------------------------------------------------------------
99 /**
100 * Get an IsNull instance.
101 * @param <T> the predicate argument type.
102 * @return IsNull
103 */
104 public static <T> IsNull<T> instance() {
105 return new IsNull<T>();
106 }
107
108 /**
109 * Get a BinaryPredicate that matches if the left argument is null.
110 * @param <A> the left {@code BinaryPredicate} argument type.
111 * @return BinaryPredicate
112 */
113 public static <A> BinaryPredicate<A, Object> left() {
114 return IgnoreRightPredicate.adapt(new IsNull<A>());
115 }
116
117 /**
118 * Get a BinaryPredicate that matches if the right argument is null.
119 * @param <A> the right {@code BinaryPredicate} argument type.
120 * @return BinaryPredicate
121 */
122 public static <A> BinaryPredicate<Object, A> right() {
123 return IgnoreLeftPredicate.adapt(new IsNull<A>());
124 }
125
126 }