线程安全高效的单例模式

class SingleTon{
    private static SingleTon singleTon = null;
    private SingleTon(){
        System.out.println("单例模式");
    }
    public static SingleTon getInstance(){
        if(singleTon==null){
            synchronized (SingleTon.class){
                if(singleTon==null){
                    singleTon = new SingleTon();
                }
            }
        }
        return singleTon;
    }
}