Question about ActionListener

[Yanxin Zhao]

Hi: everyone
I got a problem about ActionListener.
I want to use a button to control a JTextField in another class. but I am not sure how to do it. I do not know what's problem about my code, but I can not implement what I want to do.

  
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
 
public class Test4 extends JFrame{
    JTextField tf;
    JPanel jp;
 
    public Test4(){
        super("Test");
        tf = new JTextField(10);
        jp = new TestPanel();
        
    }
 
    public void buildGUI(){
        getContentPane().setLayout(new BorderLayout());
        getContentPane().add(tf, BorderLayout.CENTER);
        getContentPane().add(jp, BorderLayout.SOUTH);
        setSize(200,200);
        setVisible(true);
    }
 
    public static void main(String args[]){
        new Test4().buildGUI();
    }
}
 

class TestPanel extends JPanel{
    JButton jb;
    public TestPanel(){
        jb = new JButton("Button");
        setLayout(new FlowLayout());
        add(jb);
        ActionListener l = new ActionListener(){
             public void actionPerformed(ActionEvent e){
                 if(e.getSource() == jb){
                     new Test4().tf.setText("HelloWorld");
                 }
             }
         }; 
 
        jb.addActionListener(l);
     }
}

[Ben Wood]

Hi,

To my thinking the easiest way to get this working would be to have the GUI stuff in one class. So I've defined a MyGUI class, which is controlled by a MyGUIApp class.

 
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
 
public class MyGUI extends JFrame implements ActionListener{
    JTextField tf;
    JPanel jp;
    JButton jb;
 
    public MyGUI(){
        super("Test");
 
        initComponents();
        buildGUI();
        setSize(200,200);
        setVisible(true);
 

    }
 
    public void initComponents()
      {
        tf = new JTextField(10);
        jb = new JButton("Button");
        jp = new JPanel();
        jb.addActionListener(this);
 
}
 
    public void buildGUI(){
  JPanel contentPane = (JPanel) this.getContentPane();
 
  jp.setLayout(new FlowLayout());
  jp.add(jb);
 
        contentPane.setLayout(new BorderLayout());
        contentPane.add(tf, BorderLayout.CENTER);
        contentPane.add(jp, BorderLayout.SOUTH);
    }
 
 public void actionPerformed(ActionEvent e){
 
 Object src = e.getSource();
  if(src == jb){
tf.setText("Hello world");
  }
 }
 
}
 

 
class MyGUIApp
  {
  public static void main(String args[]){
          new MyGUI();
    }
  }
 
 

Hope this helps a little. It may not be the most elegant solution, but it works

[J Virumbi]

Look at ur this line:

new Test4().tf.setText("HelloWorld");

The "new" keyword will be creating a new Instance of Test4 class for every click on the button. Offcourse you can not see the new GUIs bcoz u are not calling builfGUI method.

If U want set a "hello World" text in the textfield for each button click, U have to do it on the existing instance of Test4 which has built ur GUI.

I have never coded in AWT. I can solve the problem but It may not be the right practise.

Check the books coz u missed the basics.

[Yanxin Zhao]

Thanks so much for your reply, Ben and J.
J, you are right, I did not realized that before. thanks so much for you reply my question so fast, Ben and J. you are save me much time. really thanks.