/*
 * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
 *
 * The MIT License
 * Copyright © 2014-2022 Ilkka Seppälä
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package com.iluwatar.singleton;

/**
 * <p>Bill Pugh Singleton Implementation.</p>
 *
 * <p>This implementation of the singleton design pattern takes advantage of the
 * Java memory model's guarantees about class initialization. Each class is
 * initialized only once, when it is first used. If the class hasn't been used
 * yet, it won't be loaded into memory, and no memory will be allocated for
 * a static instance. This makes the singleton instance lazy-loaded and thread-safe.</p>
 *
 * @author owen.leung2@gmail.com
 */
public final class BillPughImplementation {

  /**
   * Private constructor to prevent instantiation from outside the class.
   */
  private BillPughImplementation() {
    // private constructor
  }

  /**
   * The InstanceHolder is a static inner class and it holds the Singleton instance.
   * It is not loaded into memory until the getInstance() method is called.
   */
  private static class InstanceHolder {
    /**
     * Singleton instance of the class.
     */
    private static BillPughImplementation instance = new BillPughImplementation();
  }

  /**
   * Public accessor for the singleton instance.
   *
   * <p>
   * When this method is called, the InstanceHolder is loaded into memory
   * and creates the Singleton instance. This method provides a global access point
   * for the singleton instance.
   * </p>
   *
   * @return an instance of the class.
   */
  // global access point
  public static BillPughImplementation getInstance() {
    return InstanceHolder.instance;
  }
}
