What will be the output of the following code?

import java.util.*;
import java.util.concurrent.*;

class ExampleThread extends Thread {
    private static CountDownLatch latch = new CountDownLatch(1);
    private static Semaphore semaphore = new Semaphore(1, true);

    private int type;
    private String[] letters = { "A", "B", "C", "D", "E" };

    ExampleThread(int type) {
        super();
        this.type = type;
    }

    public void run() {
        try {
            if (type == 0) {
                semaphore.acquire();
                latch.countDown();
            } else {
                latch.await();
                semaphore.acquire();
            }

            for (int i = 0; i < 5; i++) {
                if (type == 0) {
                    System.out.print(i);
                } else {
                    System.out.print(letters[i]);
                }
                Thread.sleep(100);
            }
        } catch (Exception ex) {
            System.out.println("Exception 2");
        }
        semaphore.release();
    }


    public static void main(String[] args) {
        new ExampleThread(1).start();
        new ExampleThread(0).start();
    }
}
Explanation
The code flow is as follows:
The main method creates 2 threads, setting their type (via the ExampleThread constructor) to 0 and 1.
When the thread starts it checks for its type, if it's 0 - it tells the CountDownLatch object to decrement it's count field and acquires the semaphore. After the run() method execution is finished, the semaphore is released.
If the thread type is 1 - it checks the latch object's count field. If it equals to 0 - the thread execution continues, otherwise - it waits for it to become 0. Obviously, in order to acquire the semaphore, it should first be released by the 0 type thread.
Consequently, starting the code would have the 0 type thread print the numbers from 0 to 4, and the 1 type thread wait for it to finish. After the 0 type thread has released both the latch and the semaphore, the 1 type resumes and prints the letters array contents.

Follow CodeGalaxy

Mobile Beta

Get it on Google Play
Send Feedback