Referencing JPanel components from a JFrame

Question

I have an application creating a JPanel within a JFrame as follows:

public class Frame1{
    public Frame1(){
        Frame2 f2 = new Frame2();
        f2.pack();
        f2.setVisible(true);
    }

    class Frame2 extends JFrame{
        public Frame2(){
            JPanel p1 = new JPanel();
            JTextField txt1 = new JTextField("Test",12);
            p1.add(txt1);
            JButton btn1 = new JButton("Click Me!");
            p1.add(btn1);
            add(p1);
            btn1.addActionListener(this);
        }
        public void actionPerformed(ActionEvent e){
            JOptionPane.showDialog(null,text of the textbox);
        }
    }
}

Is there a way to reference the text field even though it is not a field variable and it is just declared inside the constructor (this.getRootPane().getParent() will give me the frame I believe, but where do I go from there)?

Why not make it a non-static class field if it needs to be referenced? Or find some other clean way of getting its reference such as placing it in a Map or Collection that is a non-static field? — Hovercraft Full Of Eels, Oct 17 '11 at 01:30

score 3 · Answer 1 · answered Oct 17 '11 at 01:44

Again to reiterate, why not just make your JTextField a private non-static field of the class:

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

public class Frame1 {
   public Frame1() {
      Frame2 f2 = new Frame2();
      f2.pack();
      f2.setVisible(true);
   }

   class Frame2 extends JFrame implements ActionListener {
      private JTextField txt1;

      public Frame2() {
         JPanel p1 = new JPanel();

         // JTextField txt1 = new JTextField("Test", 12);
         txt1 = new JTextField("Test", 12);

         p1.add(txt1);
         JButton btn1 = new JButton("Click Me!");
         p1.add(btn1);
         add(p1);
         btn1.addActionListener(this);
      }

      // if outside classes need to see the text
      public String getTxt1Text() {
         return txt1.getText();
      }

      public void actionPerformed(ActionEvent e) {
         JOptionPane.showMessageDialog(this, txt1.getText());
      }
   }
}

can you help me please with similar situation on https://stackoverflow.com/q/54623741/5113188 — , Feb 13 '19 at 01:48

Eng.Fouad · Answer 2 · 2011-10-17T02:09:40.130

If you want to get a reference to a JTextField that you declared it only inside the constructor, then your only option is to get it using the main JFrame, something like this:

JTextField textField = (JTextField) ((JPanel) getContentPane().getComponents()[0]).getComponents()[0];
JOptionPane.showMessageDialog(null, textField.getText());

Or for a general solution:

private JTextField textField;

getJTextField(this); // Call this from inside the constructor

// ...

private boolean getJTextField(Container c)
{
    Component[] cmps = c.getComponents();
    for (Component cmp : cmps)
    {
        if (cmp instanceof JTextField)
        {
            textField = (JTextField) cmp;
            return true;
        }
        if (cmp instanceof Container)
        {
            if(getJTextField((Container) cmp)) return true;
        }
    }
    return false;
}

However, declaring the JTextField as a class filed makes you life easier.

Referencing JPanel components from a JFrame

2 Answers2