java-design-patterns/lazy-loading/src/main/java/com/iluwatar/lazy/loading/Java8Holder.java

/*
 * 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.lazy.loading;

import java.util.function.Supplier;
import lombok.extern.slf4j.Slf4j;

/**
 * This lazy loader is thread safe and more efficient than {@link HolderThreadSafe}. It utilizes
 * Java 8 functional interface {@link Supplier} as {@link Heavy} factory.
 */
@Slf4j
public class Java8Holder {

  private Supplier<Heavy> heavy = this::createAndCacheHeavy;

  public Java8Holder() {
    LOGGER.info("Java8Holder created");
  }

  public Heavy getHeavy() {
    return heavy.get();
  }

  private synchronized Heavy createAndCacheHeavy() {
    class HeavyFactory implements Supplier<Heavy> {
      private final Heavy heavyInstance = new Heavy();

      @Override
      public Heavy get() {
        return heavyInstance;
      }
    }

    if (!(heavy instanceof HeavyFactory)) {
      heavy = new HeavyFactory();
    }

    return heavy.get();
  }
}