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

package com.iluwatar.lazy.loading;

import java.util.function.Supplier;

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

  private Supplier<Heavy> heavy = () -> createAndCacheHeavy();

  public Java8Holder() {
    System.out.println("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 (!HeavyFactory.class.isInstance(heavy)) {
      heavy = new HeavyFactory();
    }
    return heavy.get();
  }
}