public class SingletonTest { 
  //懒汉式单例类.在第一次调用的时候实例化自己  
  private SingletonTest() {} 
    private static SingletonTest single=null; 
    //静态工厂方法  
    public static SingletonTest getInstance() { 
       if (single == null) {  
         single = new SingletonTest(); 
         System.out.println("创建一次"); 
       }  
      return single; 
    } 
     
    public void show(){ 
      System.out.println("我是show"); 
    } 
 
} 

public class SingletonTest2 { 
 
  public static void main(String[] args) { 
    // TODO Auto-generated method stub 
    //故意写获取两次，创建两个对象 
    SingletonTest singleton=SingletonTest.getInstance(); 
    SingletonTest singleton2=SingletonTest.getInstance(); 
     
    //Singleton对象只创建一次，但是写两次还是可以的，而且方法都是可以调用的，但是看下面 
    singleton.show(); 
    singleton2.show(); 
     
    //两个对象的表现形式一样 
    if(singleton == singleton2){ 
      System.out.println("该对象的字符串表示形式:"); 
      System.out.println("singleton :"+singleton.toString()); 
      System.out.println("singleton2:"+singleton2.toString()); 
    } 

public class Singleton3 {  
  private static class SingletonHolder {  
    private static final Singleton3 INSTANCE = new Singleton3();  
  }  
  private Singleton3 (){}  
  public static final Singleton3 getInstance() {  
    System.out.println("singleton创建"); 
    return SingletonHolder.INSTANCE;  
  }  
}  

Singleton3 singleton3=Singleton3.getInstance(); 
    Singleton3 singleton4=Singleton3.getInstance(); 
    if(singleton3 == singleton4){ 
      System.out.println("该对象的字符串表示形式:"); 
      System.out.println("singleton3:"+singleton3.toString()); 
      System.out.println("singleton4:"+singleton4.toString()); 
    } 

QuBie qb1=new QuBie(); 
    QuBie qb2=new QuBie(); 
    if(qb1 == qb2){ 
      System.out.println("该对象的字符串表示形式:"); 
      System.out.println("singleton3:"+qb1.toString()); 
      System.out.println("singleton4:"+qb2.toString()); 
    }else{ 
      System.out.println("该对象的字符串表示形式:"); 
      System.out.println("singleton3:"+qb1.toString()); 
      System.out.println("singleton4:"+qb2.toString()); 
    } 

public class Singleton1 { 
 private Singleton1() {} 
 private static final Singleton1 single = new Singleton1(); 
 //静态工厂方法  
 public static Singleton1 getInstance() { 
   return single; 
 } 
}