Java-如何实现线程同步？

public class TestSynchonized {
    static StringBuffer s = new StringBuffer("Hello");
    public static void main(String args[]){
        MyThread t = new MyThread();
        t.start();
        MyThread.MoidfyString(s);
        System.out.println("main------"+s);
    }
}

class MyThread extends Thread{
    public void run(){
        MyThread.MoidfyString(TestSynchonized.s);
    }  
    public synchronized static void  MoidfyString(StringBuffer s){
        //s = s+"World";
        s.append("World");
        System.out.println("thread-----"+s);
    }
}