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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  }