public class ThreadPoolTest {
    public static void main(String[] args) {
        ExecutorService executorService = Executors.newCachedThreadPool();
        for (int i = 1; i <=10 ; i++) {
            final int task = i;
            executorService.execute(new Runnable() {
                @Override
                public void run() {
                    for (int j = 1; j <= 10; j++) {
                        try {
                            Thread.sleep(10);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        System.out.println(Thread.currentThread().getName() + "   is for    " + "   j=  " + j +"    task =   " + task);
                    }
                }
            });
        }
        //executorService.shutdown();
    }
}
代码很简单就不解释了

看一下第二种方式

public class SemaphoreTest {
    public static void main(String[] args) {
        ExecutorService service = Executors.newCachedThreadPool();
        final Semaphore s = new Semaphore(3);
        for (int i = 0; i < 10; i++) {// 开是个对象
            Runnable runnable = new Runnable() {
                @Override
                public void run() {
                    try {
                        s.acquire();// 判断对象的信号灯，亮就代表有线程
                    }catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println("线程" + Thread.currentThread() + "进入，当前已有" + s.availablePermits());
                    try {
                        Thread.sleep((long)(Math.random()*10000));
                    }catch (InterruptedException e){
                        e.printStackTrace();
                    }
                    System.out.println("线程"+Thread.currentThread()+"即将离开");
                    s.release();
                    System.out.println("线程"+Thread.currentThread()+"线程已离开,当前已有"+s.availablePermits());
                }
            };
            service.execute(runnable);// 把对象装线程池
        }
    }
}