setText() not working

[Vishnu Sharma]

In my application, i have made one JButton, named "Clear", i have placed its handler named ClearHandler in other file with ClearHandler.java. The functionality of the handler is, whenever button is pressed, it should clear all the textfields. For which, i have used following code:

import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
class ClearHandler extends GUIApps implements ActionListener{
public void actionPerformed(ActionEvent e){
String s="";
idfield.setText(s);
descfield.setText(s);
ratefield.setText(s);
quantfield.setText(s);
unitfield.setText(s);
System.out.print("Event:="+e.getActionCommand());
}
}

i am not able to get the functionality. after pressing button, i am getting on console, "Event: Clear", but no textfield is getting cleared. Please provide solution.

[Michael Dunn]

> Please provide solution

please provide code:
1) adding actionListener to the button, or
2) how mentioned textfields are 'seen' by ClearHandler

[Vishnu Sharma]

Michael Dunn wrote:> Please provide solution

please provide code:
1) adding actionListener to the button, or
2) how mentioned textfields are 'seen' by ClearHandler

Code for ClearHandler is i already pasted in previous quote. The text fields are not getting cleared. Whatever value i am putting into them, it should be cleared after pressing the button. But it is not happening.

[pete stein]

Michael provides a big hint when he asks how the textfields are "seen" by this class, and per your code it appears that this class in fact has no way of seeing or getting a reference to the JTextFields. Because of this, I am surprised that this class even compiles.

A suggestion:
1) Give your GUI class, the one that holds the JTextFields, a public method, say clearTextFields(), and inside this method do just that, set all the JTextField texts to "".
2) Give your ClearHandler class a GUI variable and in the ClearHandler constructor, pass a reference to the main GUI.
3) In the ClearHandler's actionPerformed method call the clearTextFields() method off of the GUI.

edit: OK, I see why your code compiles and what you're doing wrong. Your handler class extend from the gui class, and yes by doing this it will "see" the fields of the gui, but you must understand that these JTextFields that handler sees are handler's own non-displayed JTextFields and have nothing to do with the ones that are held by the GUIApps object that is displayed, that the handler class inherits completely different objects. You don't use inheritance for this for as you're seeing it simply doesn't work and it's wrong because the Handler class does not fulfill the "is-a" requirement for inheritance: in other words, it isn't inherently a more specialsed type of the GUIApps class and never will be. Instead, pass a reference from the actual GUI to your class as I suggest above and demonstrate below:

e.g.,

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

public class TestClearHandler {
   private static void createAndShowUI() {
      // create a new GUI object for display
      GUIApps gui = new GUIApps();

      // create a ClearHandler object and pass a reference from the GUI into the
      // handler via a constructor parameter
      ClearHandler handler = new ClearHandler(gui);

      // Add the ActionListener (handler object) into the GUI 
      gui.addClearHandler(handler);

      JFrame frame = new JFrame("TestClearHandler");
      frame.getContentPane().add(gui);
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      java.awt.EventQueue.invokeLater(new Runnable() {
         public void run() {
            createAndShowUI();
         }
      });
   }
}

class GUIApps extends JPanel {
   private static final String[] texts = {"Fee", "Fi", "Fo", "Fum"};
   private static final int FIELD_COUNT = texts.length;
   private JTextField[] fields = new JTextField[FIELD_COUNT];
   private JButton clearFieldsBtn = new JButton("Clear Fields");

   public GUIApps() {
      for (int i = 0; i < fields.length; i++) {
         fields[i] = new JTextField(texts[i], 8);
         add(fields[i]);
      }
      add(clearFieldsBtn);
   }

   // this allows outside classes to add handler as an action listener for the JButton
   public void addClearHandler(ActionListener al) {
      clearFieldsBtn.addActionListener(al);
   }

   // public method to clear text fields
   // I like having the GUI itself decide which text fields to clear and how
   // since this way if the GUI changes and new JTextFields are added, I don't
   // have to make any changes to the handler class at all.
   public void clearTextFields() {

      // if the GUI were displaying your JTextFields, you'd uncomment this code
      // String s="";
      // idfield.setText(s);
      // descfield.setText(s);
      // ratefield.setText(s);
      // quantfield.setText(s);
      // unitfield.setText(s);
      
      for (JTextField field : fields) {
         field.setText("");
      }
   }
}

class ClearHandler implements ActionListener {
   private GUIApps gui; // holds a reference to the actual GUI

   public ClearHandler(GUIApps gui) {
      this.gui = gui; // set that reference in the constructor
   }

   public void actionPerformed(ActionEvent arg0) {
      // call the GUI's public method to clear its text fields
      gui.clearTextFields();
   }
}

[Vishnu Sharma]

Thanks a lot pete.