001/*
002 * The MIT License
003 * Copyright (c) 2012 Microsoft Corporation
004 *
005 * Permission is hereby granted, free of charge, to any person obtaining a copy
006 * of this software and associated documentation files (the "Software"), to deal
007 * in the Software without restriction, including without limitation the rights
008 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
009 * copies of the Software, and to permit persons to whom the Software is
010 * furnished to do so, subject to the following conditions:
011 *
012 * The above copyright notice and this permission notice shall be included in
013 * all copies or substantial portions of the Software.
014 *
015 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
016 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
017 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
018 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
019 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
020 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
021 * THE SOFTWARE.
022 */
023
024package microsoft.exchange.webservices.data.core;
025
026/**
027 * Wrapper class for lazy members. Does lazy initialization of member on first
028 * access.
029 *
030 * @param <T> Type of the lazy member
031 *            <p>
032 *            If we find ourselves creating a whole bunch of these in our code,
033 *            we need to rethink this. Each lazy member holds the actual member
034 *            and a delegate. That can turn into a whole lot of overhead
035 *            </p>
036 */
037public class LazyMember<T> {
038
039  /**
040   * The lazy member.
041   */
042  private volatile T lazyMember;
043
044  /**
045   * The lazy implementation.
046   */
047  private final ILazyMember<T> lazyImplementation;
048
049  /**
050   * Public accessor for the lazy member. Lazy initializes the member on first
051   * access
052   *
053   * @return the member
054   */
055  public T getMember() {
056    T result = this.lazyMember;
057    if (result == null) {  // first check (no locking)
058      synchronized (this) {
059        result = this.lazyMember;
060        if (result == null) { // second check (with locking)
061          this.lazyMember = result = lazyImplementation.createInstance();
062        }
063      }
064    }
065    return result;
066  }
067
068  /**
069   * Constructor.
070   *
071   * @param lazyImplementation The initialization delegate to call for the item on first
072   *                           access
073   */
074  public LazyMember(ILazyMember<T> lazyImplementation) {
075    this.lazyImplementation = lazyImplementation;
076  }
077}