java - Why does the FirstThread always run before the SecondThread in the following code?

Question

public class TowThreads {
    public static class FirstThread extends Thread {
        public void run() {
            for (int i = 2; i < 100000; i++) {
                if (isPrime(i)) {
                    System.out.println("A");
                    System.out.println("B");
                }
            }
        }

        private boolean isPrime(int i) {
            for (int j = 2; j < i; j++) {
                if (i % j == 0)
                    return false;
            }
            return true;
        }
    }

    public static class SecondThread extends Thread {
        public void run() {
            for (int j = 2; j < 100000; j++) {
                if (isPrime(j)) {
                    System.out.println("1");
                    System.out.println("2");
                }
            }
        }

        private boolean isPrime(int i) {
            for (int j = 2; j < i; j++) {
                if (i % j == 0)
                    return false;
            }
            return true;
        }
    }

    public static void main(String[] args) {
        new FirstThread().run();
        new SecondThread().run();
    }
}

The output shows that the FirstThread always runs before the SecondThread which is opposite from the article I read.

Why?Must the first thread run before the second thread? If not, could you show me a good example? Thanks.

Answer 1

Use start not run

public static void main(String[] args) {
        new FirstThread().start();
        new SecondThread().start();
    }

If you use run method, you call first method and after second method. If you want to run parallel threads, you must use start method of thread.