Java在线程/代码编译调试中需要帮助

Question

Question2: I have almost same question but with Threads here is the code:

public class Example5 implements Runnable {
      static int a=0;

  public Example5() {
      a++;
  }
  public int getA() {
      return (a);
  }
  public void run() {
      System.out.println(getA());
  }

  public static void main(String[] s) {
      Example5 ex1 = new Example5();
      new Thread(ex1).start();

      Example5 ex2 = new Example5();
      new Thread (ex2).start();
  }
}

it says to me it must print: 1 or 2 2 anyone can explain this in threads.

Also anyone can explain to me what happen when i do for example(Not related to first question)

Thread t = new Thread();
t.start();
Thread t2 = new Thread();
t2.start();

Do they work sorted, (like first thread works first and then second thread) or it just goes randomly. thanks

Answer 1

Example5 ex1 = new Example5(); // a = 1
new Thread(ex1).start();  // start a new thread that will execute independently from current thread

Example5 ex2 = new Example5(); // a = 2 (a is static hence shared)
new Thread (ex2).start(); // start a new thread again

// thread1 and thread2 finish (the order is not determined - could be 
// thread2 first, then thread1)
// prints: 2 2
// If Thread1 finishes before the second "new Example5()" completes
// prints: 1 2

For the last question: kind of randomly. Since there is no synchronisation between your 3 threads (current, spawned thread1, spawn thread2).