java ProcessKeyEvent

I don't know how to use KeyEvent.
If you execute the code below,

enableEvents (long) will be accessed protected by Component

said the error.

I think it's a basic question, but I couldn't find it when I searched for it, so I asked.
How should I describe it?Please give me your wisdom...

public class Sample
{
  public static void main(String[]args) {
    javax.swing.JFrame.enableEvents(java.awt.AWTEvent.KEY_EVENT_MASK);
  }
  protected void processKeyEvent(java.awt.event.KeyEvent){
    System.out.println("key pressed");
  }
}

java

2022-09-30 21:19

2 Answers

The KeyEvent adds KeyListener to the component, where it is most likely used.

For more information, the tutorial How to Write a Key Listener (The Java™ Tutorials > Creating a GUI With JFC/Swing > Writing Event Listens) will help.

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

public classKeyEventTest{
  public static void main(String[]args) {
    EventQueue.invokeLater(()->{
      JFrame f = new JFrame();
      f.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
      f.addKeyListener(){
        @Override public void keyPressed (KeyEvente) {
          System.out.println("Called when key pressed."+e);
        }
        @Override public void keyReleased (KeyEvente) {
          System.out.println("Called when key is released."+e);
        }
        @Override public void keyTyped (KeyEvente) {
          System.out.println("Called when key is typed."+e);
        }
      });
      f.setSize (320,240);
      f.setLocationRelativeTo(null);
      f.setVisible(true);
    });
  }
}

2022-09-30 21:19

First, you have to think about the purpose of keystrokes.
As far as I can see from the code, it seems to be a sample that I just want to accept keystrokes for JFrame.
You should use KeyListener because you want to receive keystrokes from outside the component, as other answers say.
However, I think you used processKeyEvent after looking at some introductory book or website, so I will show you how to do it.

import java.awt.*;
import java.awt.event.*;

class Sample extensions JFrame {
  public static void main(String[]args) {
    Sample frame = new Sample();
    frame.setVisible(true);
  }

  Sample() {
    enableEvents(AWTEvent.KEY_EVENT_MASK);
  }
  public void processKeyEvent(KeyEvent){
    System.out.println("key pressed");
  }
}

The processKeyEvent method is defined internally to define its own components.Therefore, it must be overridden within the Component subclass as described above.There is no point in implementing it in a class that does not inherit anything, and it is not invoked on its own.
Similarly, enableEvents are also invoked from within the Component subclass.That's why it's protected.

2022-09-30 21:19

If you have any answers or tips

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