如何修复无限弹出多个窗口然后突然终止程序的 GUI 应用程序的输出？

Question

I have a problem with this GUI application I am trying to run. It converts foot to inches. But for some reason it doesn't seem to work. When i run it, multiple window pops up and the number of those windows keeps on increasing until it abruptly stops running. Please, help! Also I use netbeans.

Code for simple gui:

package converter;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class Converter{
    JFrame f;
    JTextField t1, t2;
    public Converter() {
        f = new JFrame("Converter");
        f.setSize(250, 200);
        f.setLayout(new FlowLayout());
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        JPanel p1 = new JPanel();
        JLabel foot = new JLabel("Foot");
        t1 = new JTextField(12);
        p1.add(foot);p1.add(t1);
        
        JPanel p2 = new JPanel();
        JButton btn = new JButton("Convert to Inch");
        p2.add(btn);
        
        JPanel p3 = new JPanel();
        JLabel inch = new JLabel("Inch");
        t2 = new JTextField(12);
        p3.add(inch);p3.add(t2);
        
        ButtonListener o = new ButtonListener();
        btn.addActionListener(o);
        
        f.add(p1);
        f.add(p2);
        f.add(p3);
        f.setVisible(true);
        
      

    }
    
    class ButtonListener implements ActionListener{
    @Override
    public void actionPerformed(ActionEvent e) {
           
           String t = t1.getText();
           int a = Integer.parseInt(t);
           int y = a*12;
           t1.setText(y+"");
           
           
    }
}
    public static void main(String[] args) {
     new Converter();
        
    }
    
}

Answer 1

Even though the main question was already answered in the comments, this is the answer to your additional question from the comments.

For further explanation, check the comments in the code.

public class Converter implements ActionListener {

    JFrame f;
    JTextField t1, t2;
    
    public Converter() {
        f = new JFrame("Converter");
        f.setSize(250, 200);
        f.setLayout(new FlowLayout());
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    
        JPanel p1 = new JPanel();
        JLabel foot = new JLabel("Foot");
        t1 = new JTextField(12);
        p1.add(foot);
        p1.add(t1);
    
        JPanel p2 = new JPanel();
        JButton btn = new JButton("Convert to Inch");
        p2.add(btn);
    
        JPanel p3 = new JPanel();
        JLabel inch = new JLabel("Inch");
        t2 = new JTextField(12);
        p3.add(inch);
        p3.add(t2);
        // Here add the action listener to you button
        // In this case "this" because your "Converter" is your ActionListener
        btn.addActionListener(this);
    
        f.add(p1);
        f.add(p2);
        f.add(p3);
        f.setVisible(true);
    
    }
    
    // Override the actionPerformed method in your Converter Class (as it now
    // implements ActionListener)
    @Override
    public void actionPerformed(ActionEvent e) {
        String t = t1.getText();
        int a = Integer.parseInt(t);
        int y = a * 12;
        t2.setText(y + "");
    }
    
    public static void main(String[] args) {
        new Converter();
    }
}