01: /*
02: * Copyright 2001-2004 The Apache Software Foundation
03: *
04: * Licensed under the Apache License, Version 2.0 (the "License");
05: * you may not use this file except in compliance with the License.
06: * You may obtain a copy of the License at
07: *
08: * http://www.apache.org/licenses/LICENSE-2.0
09: *
10: * Unless required by applicable law or agreed to in writing, software
11: * distributed under the License is distributed on an "AS IS" BASIS,
12: * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13: * See the License for the specific language governing permissions and
14: * limitations under the License.
15: */
16: package org.apache.commons.collections.functors;
17:
18: import java.io.Serializable;
19:
20: import org.apache.commons.collections.Predicate;
21:
22: /**
23: * Predicate implementation that returns true if the input is null.
24: *
25: * @since Commons Collections 3.0
26: * @version $Revision: 348444 $ $Date: 2005-11-23 14:06:56 +0000 (Wed, 23 Nov 2005) $
27: *
28: * @author Stephen Colebourne
29: */
30: public final class NullPredicate implements Predicate, Serializable {
31:
32: /** Serial version UID */
33: private static final long serialVersionUID = 7533784454832764388L;
34:
35: /** Singleton predicate instance */
36: public static final Predicate INSTANCE = new NullPredicate();
37:
38: /**
39: * Factory returning the singleton instance.
40: *
41: * @return the singleton instance
42: * @since Commons Collections 3.1
43: */
44: public static Predicate getInstance() {
45: return INSTANCE;
46: }
47:
48: /**
49: * Restricted constructor.
50: */
51: private NullPredicate() {
52: super ();
53: }
54:
55: /**
56: * Evaluates the predicate returning true if the input is null.
57: *
58: * @param object the input object
59: * @return true if input is null
60: */
61: public boolean evaluate(Object object) {
62: return (object == null);
63: }
64:
65: }
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