设计模式之单例模式

1、饿汉式

public class HungerSingleObject {
  private static HungerSingleObject instance = new HungerSingleObject();
  private HungerSingleObject() {		
  }
  public static HungerSingleObject getInstance() {
    return instance;
  }
  public void showMessage() {
    System.out.println("this is singleton pattern");
  }
}

2、懒汉式 线程不安全

public class LazySingleObject {
  private static LazySingleObject instance;
  private LazySingleObject() {

  }
  public static LazySingleObject getInstance() {
    if(instance == null) {
      instance = new LazySingleObject();
    }
    return instance;
  }
  public void showMessage() {
    System.out.println("this is lazy single pattern");
  }
}

3、懒汉式 线程安全 加同步锁

public class SyncLazySingleObject {
  private static SyncLazySingleObject instance;
  private SyncLazySingleObject() {}
  public static synchronized SyncLazySingleObject getInstance() {
    if(instance == null) {
      instance = new SyncLazySingleObject();
    }
    return instance;
  }
  public void showMessage() {
    System.out.println("this is synchronized lazy single pattern");
  }
}