How to Intercept Key Events in Java

The "KeyEvent" Java event triggers each time a user presses a keyboard key while your application runs on the computer. You can intercept a key event and perform other code processes after the user presses any key. Keylogger programs use this event feature, but most programmers use this feature to detect incorrect input characters. For instance, the KeyEvent lets you detect if a user presses a letter key in a text box that only allows numbers.

Instructions

1. Right-click the Java source code file you want to edit, click "Open With" and choose your Java editor in the list of programs.

2. Add a "listener" to a text box. The listener triggers when the user places the cursor in the text box and presses a key. The following code adds a listener:

   textbox1.addKeyListener(this);

3. Replace "textbox1" with the name of your own text box.

4. Create the function that triggers when the user presses a key. In this example, Java prints the key pressed to the user's screen:

   public void keyTyped(KeyEvent e) {

   char key = e.getKeyChar();

   System.out.println("You pressed the " + key + " key.");

   }

References

• Oracle: How to Write a Key Listener

Resources

• Read this Article in Spanish