001/*
002 *  Licensed to the Apache Software Foundation (ASF) under one
003 *  or more contributor license agreements.  See the NOTICE file
004 *  distributed with this work for additional information
005 *  regarding copyright ownership.  The ASF licenses this file
006 *  to you under the Apache License, Version 2.0 (the
007 *  "License"); you may not use this file except in compliance
008 *  with the License.  You may obtain a copy of the License at
009 *
010 *    http://www.apache.org/licenses/LICENSE-2.0
011 *
012 *  Unless required by applicable law or agreed to in writing,
013 *  software distributed under the License is distributed on an
014 *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 *  KIND, either express or implied.  See the License for the
016 *  specific language governing permissions and limitations
017 *  under the License.
018 *
019 */
020package org.apache.mina.util;
021
022/**
023 * An abstract class which provides semantics for an object which will be only
024 * fully initialized when requested to. It allows to avoid loosing time when 
025 * early initializing unnecessary objects.
026 * 
027 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
028 * @since MINA 2.0.0-M2
029 */
030public abstract class LazyInitializer<V> {
031
032    /**
033     * The value that results on the {@link #init()} call. If null,
034     * it means that the value has not been initialized yet.
035     */
036    private V value;
037
038    /**
039     * Initializes the value.
040     *
041     * @return the initialized value
042     */
043    public abstract V init();
044
045    /**
046     * @return the value resulting from the initialization.
047     */
048    public V get() {
049        if (value == null) {
050            value = init();
051        }
052
053        return value;
054    }
055}