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.Transformer;
21:
22: /**
23: * Transformer implementation that returns the same constant each time.
24: * <p>
25: * No check is made that the object is immutable. In general, only immutable
26: * objects should use the constant factory. Mutable objects should
27: * use the prototype factory.
28: *
29: * @since Commons Collections 3.0
30: * @version $Revision: 348444 $ $Date: 2005-11-23 14:06:56 +0000 (Wed, 23 Nov 2005) $
31: *
32: * @author Stephen Colebourne
33: */
34: public class ConstantTransformer implements Transformer, Serializable {
35:
36: /** Serial version UID */
37: private static final long serialVersionUID = 6374440726369055124L;
38:
39: /** Returns null each time */
40: public static final Transformer NULL_INSTANCE = new ConstantTransformer(
41: null);
42:
43: /** The closures to call in turn */
44: private final Object iConstant;
45:
46: /**
47: * Transformer method that performs validation.
48: *
49: * @param constantToReturn the constant object to return each time in the factory
50: * @return the <code>constant</code> factory.
51: */
52: public static Transformer getInstance(Object constantToReturn) {
53: if (constantToReturn == null) {
54: return NULL_INSTANCE;
55: }
56: return new ConstantTransformer(constantToReturn);
57: }
58:
59: /**
60: * Constructor that performs no validation.
61: * Use <code>getInstance</code> if you want that.
62: *
63: * @param constantToReturn the constant to return each time
64: */
65: public ConstantTransformer(Object constantToReturn) {
66: super ();
67: iConstant = constantToReturn;
68: }
69:
70: /**
71: * Transforms the input by ignoring it and returning the stored constant instead.
72: *
73: * @param input the input object which is ignored
74: * @return the stored constant
75: */
76: public Object transform(Object input) {
77: return iConstant;
78: }
79:
80: /**
81: * Gets the constant.
82: *
83: * @return the constant
84: * @since Commons Collections 3.1
85: */
86: public Object getConstant() {
87: return iConstant;
88: }
89:
90: }
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