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.collections.functors;
18
19 import java.io.Serializable;
20
21 import org.apache.commons.collections.Factory;
22
23 /**
24 * Factory implementation that returns the same constant each time.
25 * <p>
26 * No check is made that the object is immutable. In general, only immutable
27 * objects should use the constant factory. Mutable objects should
28 * use the prototype factory.
29 *
30 * @since 3.0
31 * @version $Id: ConstantFactory.java 1435965 2013-01-20 21:13:18Z tn $
32 */
33 public class ConstantFactory<T> implements Factory<T>, Serializable {
34
35 /** Serial version UID */
36 private static final long serialVersionUID = -3520677225766901240L;
37
38 /** Returns null each time */
39 public static final Factory<Object> NULL_INSTANCE = new ConstantFactory<Object>(null);
40
41 /** The closures to call in turn */
42 private final T iConstant;
43
44 /**
45 * Factory method that performs validation.
46 *
47 * @param <T> the type of the constant
48 * @param constantToReturn the constant object to return each time in the factory
49 * @return the <code>constant</code> factory.
50 */
51 @SuppressWarnings("unchecked")
52 public static <T> Factory<T> constantFactory(final T constantToReturn) {
53 if (constantToReturn == null) {
54 return (Factory<T>) NULL_INSTANCE;
55 }
56 return new ConstantFactory<T>(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 ConstantFactory(final T constantToReturn) {
66 super();
67 iConstant = constantToReturn;
68 }
69
70 /**
71 * Always return constant.
72 *
73 * @return the stored constant value
74 */
75 public T create() {
76 return iConstant;
77 }
78
79 /**
80 * Gets the constant.
81 *
82 * @return the constant
83 * @since 3.1
84 */
85 public T getConstant() {
86 return iConstant;
87 }
88
89 }