java - Thread and JLabel in Swing- Not working properly

Question

Please look at the code below.

import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JFrame;
import javax.swing.JPanel;

class thread_jishu extends Thread{
    @Override
    public void run(){
        int p=-1;
        for(;;){
            //here continuously checking that whether
            //the value of label_thread.i is equals to p or not

            if(label_thread.i!=p){
                try{
                    Thread.sleep(1000);
                }catch(Exception e){}

                label_thread.lb.setText("after sleeping at -> "+label_thread.i);
                // here i want to set the JLabel
                // text after waiting 1sec only when
                // label_thread.i has been changed,
                // but not happening 
                p=label_thread.i;
            }
        }
    }
}

public class label_thread  implements java.awt.event.ActionListener{

    /**
     * @param evt
     */
    @Override
    public void actionPerformed(java.awt.event.ActionEvent evt){
        i+=1;
        lb.setText("Button clicked at -> "+i);
    }

    static int i=-1;
    static JLabel lb=new JLabel("hello here");
    static JFrame window=new JFrame("Jishu");
    static JFrame window2=new JFrame("Jishu");

    public static void main(String[] args) {
        // TODO code application logic here
        new thread_jishu().start();
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        window.setMinimumSize(new java.awt.Dimension(200,200));

        JButton bt=new JButton("Click here");
        bt.addActionListener(new label_thread());
        JPanel panel=new JPanel();
        panel.add(bt);
        window.add(panel);
        window2.add(lb);
        window.setVisible(true);
        window2.setVisible(true);
        window2.setMinimumSize(new java.awt.Dimension(200,200));
    }

}

I want to reset the JLabel in the 2nd window when the value of i is not equals to p that means the button is clicked in 1st window.

But when button is clicked JLabel's text is not being changed.

Answer 1

Swing elements should not be modified outside of the AWT event thread. You can use SwingUtilities.invokeLater if you'd like to execute code in the AWT event thread.

Something like:

SwingUtilities.invokeLater(new Runnable() {
    @override
    public void run() {
        //Swing stuff here.
    }
});

would get you pretty close.