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1   /*
2    *  Licensed to the Apache Software Foundation (ASF) under one
3    *  or more contributor license agreements.  See the NOTICE file
4    *  distributed with this work for additional information
5    *  regarding copyright ownership.  The ASF licenses this file
6    *  to you under the Apache License, Version 2.0 (the
7    *  "License"); you may not use this file except in compliance
8    *  with the License.  You may obtain a copy of the License at
9    *
10   *    http://www.apache.org/licenses/LICENSE-2.0
11   *
12   *  Unless required by applicable law or agreed to in writing,
13   *  software distributed under the License is distributed on an
14   *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15   *  KIND, either express or implied.  See the License for the
16   *  specific language governing permissions and limitations
17   *  under the License.
18   *
19   */
20  package org.apache.mina.util;
21  
22  /**
23   * An abstract class which provides semantics for an object which will be only
24   * fully initialized when requested to. It allows to avoid loosing time when 
25   * early initializing unnecessary objects.
26   * 
27   * @author <a href="http://mina.apache.org">Apache MINA Project</a>
28   * @since MINA 2.0.0-M2
29   */
30  public abstract class LazyInitializer<V> {
31  
32      /**
33       * The value that results on the {@link #init()} call. If null,
34       * it means that the value has not been initialized yet.
35       */
36      private V value;
37  
38      /**
39       * Initializes the value.
40       *
41       * @return the initialized value
42       */
43      public abstract V init();
44  
45      /**
46       * Returns the value resulting from the initialization.
47       * @return the initialized value
48       */
49      public V get() {
50          if (value == null) {
51              value = init();
52          }
53  
54          return value;
55      }
56  }