import java.util.*;
public class Main {
    static ArrayList<Integer> list=new ArrayList<Integer>();
    private static Object lock=new Object();
    private static int a=1;
    private static int b=1;
    static boolean bool=true;
    public static void main(String[] args)
    {
        Thread t1
 
=new Thread(){
            public void run()
            {
                for(int i=0;i<10;i++)
                {
                    synchronized(lock)
                    {                        
                        a*=3;
                        list.add(a);
                        bool=false
 
;
                        lock.notify();//喚醒一個線程
                        try
                        {
                            lock.wait();//掛起該線程
                        }
                        catch(InterruptedException e)
                        {
                                e.printStackTrace();
                        }

                    }
                }
            }
        };
        Thread t2
 
=new Thread(){
            public void run()
            {
                for(int i=0;i<10;i++)
                {
                    synchronized(lock){
                        if(bool)
                        {
                            try{
                                lock.wait();
                            }
                            catch(InterruptedException e)
                            {
                                e.printStackTrace();
                            }
                        }
                        b*=7;
                        list.add(b);
                        bool=true;
                        lock.notifyAll();//喚醒所有等待線程（同一個鎖上）
                    }
                }
            }
            
        };
        t1.start();
        t2.start();
        try
        {
            t1.join();
            t1.join();
        }
        catch(InterruptedException e)
        {
            e.printStackTrace();
        }
        for(int i=0;i<list.size();i++)
        {
            System.out.println(list.get(i));
        }
    }

}

兩個線程，交替執行