Programmatically trigger a key events in a JTextField?

Question

How do I programmatically trigger a key pressed event on a JTextField that is listening for events on the ENTER?

The listener for key events on my JTextField is declared as follows:

myTextField.addKeyListener(new KeyAdapter() {

    @Override
    public void keyTyped(KeyEvent e) {
        if (e.getKeyChar() == KeyEvent.VK_ENTER) {
            // Do stuff
        }
    }
});

Thanks.

Solution 1

• Do not use KeyListener on JTextField simply add ActionListener which will be triggered when ENTER is pressed (thank you @robin +1 for advice)

  JTextField textField = new JTextField();
  
  textField.addActionListener(new ActionListener() {
      @Override
      public void actionPerformed(ActionEvent ae) {
           //do stuff here when enter pressed
      }
  });
  

• To trigger KeyEvent use requestFocusInWindow() on component and use Robot class to simulate key press

Like so:

textField.requestFocusInWindow();

try { 
    Robot robot = new Robot(); 

    robot.keyPress(KeyEvent.VK_ENTER); 
} catch (AWTException e) { 
e.printStackTrace(); 
} 

Example:

import java.awt.AWTException;
import java.awt.Robot;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;

public class Test {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                JTextField textField = new JTextField();

                textField.addActionListener(new ActionListener() {
                    @Override
                    public void actionPerformed(ActionEvent ae) {
                        System.out.println("Here..");
                    }
                });
                frame.add(textField);

                frame.pack();
                frame.setVisible(true);

                textField.requestFocusInWindow();

                try {
                    Robot robot = new Robot();

                    robot.keyPress(KeyEvent.VK_ENTER);
                } catch (AWTException e) {
                    e.printStackTrace();
                }
            }
        });
    }
}

UPDATE:

As others like @Robin and @mKorbel have suggested you might want a DocumentListener/DocumentFiler (Filter allows validation before JTextField is updated).

You will need this in the event of data validation IMO.

see this similar question here

it shows how to add a DocumentFilter to a JTextField for data validation. The reason for document filter is as I said allows validation before chnage is shown which is more useful IMO

Solution 2

You can construct Event by yourself and then call dispatchEvent on JTextField.

  KeyEvent keyEvent = new KeyEvent(...); //create
  myTextField.dispatchEvent();

For parameters of KeyEvent can refer KeyEvent constructors

Comments

[Robin]

-1 There is already a binding for the ENTER key. It will trigger the ActionListener attached to the text field. Overriding this might cause subtle issues

[David Kroukamp]

@Robin I see your point +1 thank you for the knowlegde.. updated code

[mKorbel]

I bet that is only about DocumentListener, dispatchEvent(); could be usefull to simulating DocumentListener from KeyListener, (now coming reason why I commenting...) or your answer going another direction, then have to add more detailed description about your idea

[mKorbel]

How do I problematically trigger a key pressed event on a JTextField :-) I bet that is only about DocumentListener, even ActionListner returns whole Document

[Nikolay Kuznetsov]

@mKorbel, can you please let me know the logical chain how you come up to DocumentListener? Because I have never used it and here it is never mentioned. But dispatchEvent() I have used for JScrollPane and it worked fine. Do you think it is not suitable in this case?

[mKorbel]

key event are implemented in Document, Document is model for JTextComponents, you can to listening all typed chars by add DocumentListener :-) never add KeyListener (my view) to Swing *JComponents, only if is there real reason e.i. combinations of 4-5 keys are pressed or for another ZOO came from keyboard

[Nikolay Kuznetsov]

@mKorbel, ok thanks, I would need to read about internals of JTextComponent. However, if the author still wants to use the code he provided us, I guess my answer might be useful to him.

[mKorbel]

hehehe I see, then OP will returns with a few question or to creating mess,

[David Kroukamp]

@mKorbel But Why go through all of that if we simply want to catch enter pressed and can via actionListener. I guess you are under the assumption the OP is performing validation checks... +1 this would be the way to go than

[mKorbel]

@David Kroukamp I'm "confused" from this question, better could be waiting for OPs whatever, nobody knows

[David Kroukamp]

@mKorbel true, though I'd lean with DocumentFilter and not Listener if it is the case

[Alex Barker]

If anyone else is wondering why the example keeps repeating the enter key, it is because robot.keyRelease(KeyEvent.VK_ENTER) is never called.

[Edu Costa]

For JUnit purpose you can customize you JTextField as explained here stackoverflow.com/questions/47336703/…