Question

I want that main should print hello (in a pop up dialogue box) everytime the button is clicked. So I designed the following program but it doesn’t seem to work. The program compiles and executes just fine but when I click the button, I don’t see the any dialogue box popping up. I have put in place the getter and setter of the boolean variable (button_clicked) whose value is being tested in the main() block.
Please help if you know..

import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

class abc extends JFrame implements ActionListener{

boolean button_clicked = false;
JButton b1;

abc(){
    this.setSize (400, 400);
    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    this.createUI();
}

void createUI(){
    this.setLayout(null);
    b1 = new JButton("x");
    b1.setSize(110,30);
    b1.setLocation(10,210);
    this.add(b1);

    b1.addActionListener(this);
}

public boolean isButton_clicked() {
    return button_clicked;
}

public void setButton_clicked(boolean button_clicked) {
    this.button_clicked = button_clicked;
}


public void actionPerformed(ActionEvent arg0) {
    button_clicked = true;

    //I don't want to print the dialogue box from here..
    //I want to keep everything under main()'s control.
}

}


public class tempMain extends JFrame {

public static void main(String[] args) {
    abc temp = new abc();
    temp.setVisible(true);
    while(true){
        if(temp.isButton_clicked())
            JOptionPane.showMessageDialog(null, "Hello");
    }
}

}

Answer 1

As has already been pointed out by a number of people, you approach and design are flawed. I won’t go into further as it has already been dealt with, but as a suggestion you could try…

abc temp = new abc();
temp.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent evt) {
        JOptionPane.showMessageDialog(null, "Look Ma, I'm in Main...");
    }
});
temp.setVisible(true);

And in your abc class…

class abc JFrame implements {
    // build your class as normal

    public void addActionListener(ActionListener listener) {
        b1.addActionListener(listener);
    }    
}