br.com.objectos.way.lazy.Lazy Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of lazy-api Show documentation

The newest version!

/*
 * Copyright 2015 Objectos, Fábrica de Software LTDA.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package br.com.objectos.way.lazy;

/**
 * @author [email protected] (Marcio Endo)
 */
public abstract class Lazy {

  private volatile boolean cached;
  private T instance;

  public final T get() {
    if (!cached) {
      synchronized (this) {
        if (instance == null) {
          instance = compute();
          if (instance == null) {
            throw new NullPointerException("Lazy computation returned a null value.");
          }
          cached = true;
        }
      }
    }
    return instance;
  }

  public final void unset() {
    cached = false;
  }

  protected abstract T compute();

}