使用newFixedThreadPool創建線程（可以傳入線程的個數）

        //使用newFixedThreadPool創建線程
        ExecutorService fixedPool = Executors.newFixedThreadPool(5);
        for (int i = 0; i <20; i++) {
            fixedPool.execute(new MyThread03(i));
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}
class MyThread03 implements Runnable{
    int num;

    public MyThread03(int num) {
        super();
        this.num = num;
    }

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName()+":"+num);
        
    }