设计模式

public class MyStaticHungrySingleton {
    private static final MyStaticHungrySingleton myStaticHungrySingleton;
    static{
        myStaticHungrySingleton = new MyStaticHungrySingleton();
    }
    private MyStaticHungrySingleton(){}
    public MyStaticHungrySingleton getInstance(){
        return myStaticHungrySingleton;
    }
}<br><br>public class MyHungrySingleton {<br>    private static final MyHungrySingleton myHungrySingleton = new MyHungrySingleton();<br><br>    private MyHungrySingleton(){}<br><br>    private MyHungrySingleton getInstance(){<br>        return myHungrySingleton;<br>    }<br>}

public class LazySimpleSingletion {
    private static LazySimpleSingletion instance;
    private LazySimpleSingletion(){}
    public synchronized static LazySimpleSingletion getInstance(){
        if(instance == null){
            instance = new LazySimpleSingletion();
        }
        return instance;
    }
}
//性能下降
public class LazyDoubleCheckSingletion {
    private volatile static LazyDoubleCheckSingletion instance;
    private LazyDoubleCheckSingletion(){}
    public static LazyDoubleCheckSingletion getInstance(){
        //检查是否要阻塞
        if(instance==null){
            synchronized (LazyDoubleCheckSingletion.class){
                //检查是否要创建实例
                if(instance==null){
                    instance = new LazyDoubleCheckSingletion();
                }
            }
        }
        return instance;
    }
}
//指令重排序