线程安全的单例

public class ThreadSafeSingleTon {
    private static ThreadSafeSingleTon instance=null;
    private ThreadSafeSingleTon(){}
    public static ThreadSafeSingleTon getInstance(){
        if(instance==null){
            synchronized (ThreadSafeSingleTon.class){
                if(instance==null){
                    instance=new ThreadSafeSingleTon();
                }
            }
        }
        return instance;
    }
}