单例

恶汉模式
public class hungrysingleton implements Serializable{
    private final static hungrysingleton h;
    static {
        h=new hungrysingleton();
    }
    private hungrysingleton(){
        if(h!=null){
            throw new RuntimeException("单利模式禁止反射");
        }

    }
    public static hungrysingleton getinstance(){
        return h;
    }
    private Object readResolve(){
        return h;
    }

}

懒汉模式

public class Lazysingle {
    private static Lazysingle lazysingle=null;

    private Lazysingle() {
    }

   public static Lazysingle getInstance(){
       if(lazysingle==null){
           synchronized (Lazysingle.class){
               if(lazysingle==null){
                   lazysingle=new Lazysingle();
               }
           }

       }
       return lazysingle;
   }
}

public class Lazysingle2 {
    private volatile static Lazysingle2 lazysingle=null;

    private Lazysingle2() {
    }

    public static Lazysingle2 getInstance(){
        if(lazysingle==null){
            synchronized (Lazysingle2.class){
                if(lazysingle==null){
                    lazysingle=new Lazysingle2();
                }
            }

        }
        return lazysingle;
    }
}