Four methods of multi-threaded sequential operation. Ask casually during the interview

The article introduces 4 Methods , Simple and easy to understand , adopt 4 individual demo throw away a brick in order to get a gem .

1、 Passing through the join() Method specifies the order

adopt join() Method to make the current thread “ Blocking ”,

“”

Running results ：

2、 Pass in main thread join() Method specifies the order

A child thread refers to a thread that occurs in Thread Internal code , The main thread refers to what happens in main Code in function . The latest multithreaded interview questions have been sorted out , Click on Java Interview database Small program online brush questions .

We can do it in main Function through join() Method lets the main thread block and wait to achieve the purpose of executing in the specified order .

public class ThreadMainJoinDemo {
    public static void main(String[] args) throws InterruptedException {
        final Thread thread1 = new Thread(new  Runnable() {
            @Override
            public void  run() {
                System.out.println( " Open the refrigerator ！");
            }
        });
 
        final Thread thread2 = new Thread(new  Runnable() {
            @Override
            public void  run() {
                System.out.println( " Take out a bottle of milk ！");
            }
        });
 
        final Thread thread3 = new Thread(new  Runnable() {
            @Override
            public void  run() {
                System.out.println( " Turn off the fridge. ！");
            }
        });
 
        thread1.start();
        thread1.join();
        thread2.start();
        thread2.join();
        thread3.start();
    }
}

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Output results ：

Open the refrigerator ！
Take out a bottle of milk ！
Turn off the fridge. ！

3、 Through the countdown timer CountDownLatch Realization

CountDownLatch More flexible control is provided through counters , As long as it is detected that the counter is 0 The current thread can execute down without taking care of the corresponding thread Whether the implementation is completed .

public class ThreadCountDownLatchDemo {
 
    private static CountDownLatch countDownLatch1 = new CountDownLatch(1);
 
    private static CountDownLatch countDownLatch2 = new CountDownLatch(1);
 
    public static void main(String[] args) {
        final Thread thread1 = new Thread(new  Runnable() {
            @Override
            public void  run() {
                System.out.println( " Open the refrigerator ！");
                countDownLatch1.countDown();
            }
        });
 
        final Thread thread2 = new Thread(new  Runnable() {
            @Override
            public void  run() {
                try {
                    countDownLatch1.await();
                    System.out.println( " Take out a bottle of milk ！");
                    countDownLatch2.countDown();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
 
        final Thread thread3 = new Thread(new  Runnable() {
            @Override
            public void  run() {
                try {
                    countDownLatch2.await();
                    System.out.println( " Turn off the fridge. ！");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
 
        // The order of the following three lines of code can be adjusted at will , The running results of the program are not affected
        thread3.start();
        thread1.start();
        thread2.start();
    }
}
Open the refrigerator ！
Take out a bottle of milk ！
Turn off the fridge. ！

Single threaded pool (newSingleThreadExecutor) The advantages of , Serial execution of all tasks .

Output results ：

Open the refrigerator ！
Take out a bottle of milk ！
Turn off the fridge. ！