還是套路問題，一種思想而已，兩種方式

　　1 dubble check instance

　　2 static inner class

 　兩次檢測加類鎖

　　靜態內部類，其實就是餓漢模式，直接給你就好了

package Concurrency;

class dubbleCheck{
    private static dubbleCheck ds ;
    public dubbleCheck getInstance(){
        if(ds == null){
            try{
                Thread.sleep(
 
50);

                synchronized (dubbleCheck.class){
                    if(ds==null){
                        ds = new dubbleCheck();
                    }
                }

            }catch (InterruptedException e){
                e.printStackTrace();
            }
        }
        return ds;
    }
    
 
protected dubbleCheck(){
    }
}
class InnerSigleton {
    private static class Sigleton{
        private static InnerSigleton is = new InnerSigleton();
    }
    public static InnerSigleton getInstance(){
        return  Sigleton.is;
    }
}