CODEWITHSUNDEEP
java
Ahmed
Ahmed

Reputation: 3458

How to share objects among threads?

there are several similar questions . But my question is basic and not specific to a problem . I want a basic code example of how to do that . Here is the code I am working on

         Controller c = new Controller(....) ;
         if(.... ) //manager
    {
        if (jRadioButton1.isSelected())
        {
          java.awt.EventQueue.invokeLater(new Runnable() {
       public void run() {
            new MyGUI().setVisible(true);//I want to pass object c to MyGUI Thread
        }
    });
        }

Upvotes: 1

Views: 3003

Answers (5)

maerics
maerics

Reputation: 156414

It can be as easy as passing the Runnables the same reference:

final Object o = new Object();
Runnable r = new Runnable() {
  public void run() {
    System.out.println(Thread.currentThread().getName() + ": " + o);
  }
};
Thread t1 = new Thread(r);
Thread t2 = new Thread(r);
t1.start();
t2.start();

Of course, there are important considerations if these threads will be modifying attributes of the shared object concurrently.

In your code example, you could simply change the MyGUI constructor to take a Controller object as an argument, or provide an instance setter method.

Upvotes: 1

Andrew T Finnell
Andrew T Finnell

Reputation: 13628

ok well to basically answer it..

Notice the change final and constructor of MyGUI

     final Controller c = new Controller(....) ;
     if(.... ) //manager
     {
          if (jRadioButton1.isSelected())
          {
             java.awt.EventQueue.invokeLater(new Runnable() {
                 public void run() {                        
                    new MyGUI(c).setVisible(true);//I want to pass object c to MyGUI Thread
             }
          });
     }

     class MyGUI
     { 
           private Controller _controller;
           public MyGui(Controller c)
           {
                _controller = c;
           }
     }

Upvotes: 1

dogbane
dogbane

Reputation: 274542

In your example, make Controller c final and then simply pass it into your GUI via the constructor or a setter method. For example:

     final Controller c = new Controller(....) ;
     if(.... ) //manager
{
    if (jRadioButton1.isSelected())
    {
      java.awt.EventQueue.invokeLater(new Runnable() {
   public void run() {
        MyGUI gui = new MyGUI(c);//pass object c to MyGUI Thread via constructor
        // gui.setController(c); //or you could have a setter method
        gui.setVisible(true);
    }

Upvotes: 1

JB Nizet
JB Nizet

Reputation: 691665

You can share anything you want between threads : as soon as a method executing in a thread has a reference to an object, and another method in another thread has a reference to the same object, then this object is shared between the two threads.

The difficulty, in this case, is to make sure every operation done on the shared object is thread-safe (i.e. doesn't put the object in a abnormal state, and returns correct values). Immutable objects are always thread-safe. Other ones often need synchronization to be thread-safe.

Upvotes: 0

Harry Joy
Harry Joy

Reputation: 59660

You don't need to do anything special to share objects between threads, any thread can access any object.

However, if you want to access an object safely from multiple threads, you need to be careful. Either the object's methods must be thread-safe, or you need to synchronize access to the object.

Hope this helps.

Upvotes: 3

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