Java - creating a new thread

Question

I'm new to threads. I wanted to create some simple function working separately from main thread. But it doesn't seem to work. I'd just like to create new thread and do some stuff there independently of what's happening on main thread. This code may look weird but I don't have much experience with threading so far. Could you explain me what's wrong with this?

  public static void main(String args[]){
      test z=new test();

      z.setBackground(Color.white);

      frame=new JFrame();
      frame.setSize(500,500);
      frame.add(z);
      frame.addKeyListener(z);
      frame.setVisible(true);

      one=new Thread(){
          public void run() {
              one.start();
              try{
                  System.out.println("Does it work?");
                  Thread.sleep(1000);
                  System.out.println("Nope, it doesnt...again.");
              } catch(InterruptedException v){System.out.println(v);}
          }
      };
  }

Answer 1

You are calling the one.start() method in the run method of your Thread. But the run method will only be called when a thread is already started. Do this instead:

one = new Thread() {
    public void run() {
        try {
            System.out.println("Does it work?");

            Thread.sleep(1000);

            System.out.println("Nope, it doesnt...again.");
        } catch(InterruptedException v) {
            System.out.println(v);
        }
    }  
};

one.start();

Answer 2

You can do like:

    Thread t1 = new Thread(new Runnable() {
    public void run()
    {
         // code goes here.
    }});  
    t1.start();

Answer 3

The goal was to write code to call start() and join() in one place. Parameter anonymous class is an anonymous function. new Thread(() ->{})

new Thread(() ->{
        System.out.println("Does it work?");
        Thread.sleep(1000);
        System.out.println("Nope, it doesnt...again.");       
}){{start();}}.join();

In the body of an anonymous class has instance-block that calls start(). The result is a new instance of class Thread, which is called join().

Answer 4

You need to do two things:

• Start the thread
• Wait for the thread to finish (die) before proceeding

ie

one.start();
one.join();

If you don't start() it, nothing will happen - creating a Thread doesn't execute it.

If you don't join) it, your main thread may finish and exit and the whole program exit before the other thread has been scheduled to execute. It's indeterminate whether it runs or not if you don't join it. The new thread may usually run, but may sometimes not run. Better to be certain.

Answer 5

Since a new question has just been closed against this: you shouldn't create Thread objects yourself. Here's another way to do it:

public void method() {
    Executors.newSingleThreadExecutor().submit(() -> {
        // yourCode
    });
}

You should probably retain the executor service between calls though.

Answer 6

There are several ways to create a thread

1. by extending Thread class >5
2. by implementing Runnable interface - > 5
3. by using ExecutorService inteface - >=8

Answer 7

If you want more Thread to be created, in above case you have to repeat the code inside run method or at least repeat calling some method inside.

Try this, which will help you to call as many times you needed. It will be helpful when you need to execute your run more then once and from many place.

class A extends Thread {
    public void run() {
             //Code you want to get executed seperately then main thread.       
    }
     }

Main class

A obj1 = new A();
obj1.start();

A obj2 = new A();
obj2.start();

Answer 8

run() method is called by start(). That happens automatically. You just need to call start(). For a complete tutorial on creating and calling threads see my blog http://preciselyconcise.com/java/concurrency/a_concurrency.php

Answer 9

A simpler way can be :

new Thread(YourSampleClass).start();    

Answer 10

Please try this. You will understand all perfectly after you will take a look on my solution.

There are only 2 ways of creating threads in java

with implements Runnable

class One implements Runnable {
@Override
public void run() {
    System.out.println("Running thread 1 ... ");
}

with extends Thread

class Two extends Thread {
@Override
public void run() {
    System.out.println("Running thread 2 ... ");
}

Your MAIN class here

public class ExampleMain {
public static void main(String[] args) {

    One demo1 = new One();
    Thread t1 = new Thread(demo1);
    t1.start();

    Two demo2 = new Two();
    Thread t2 = new Thread(demo2);
    t2.start();
}

}