MouseListener/KeyListener not working (JPanel)

I'm doing a little project that involves the mouse and key listeners in JPanel. Unfortunately, none of the methods are called when I use the mouse/keyboard. I have worked with JPanels/JFrame/JApplet and JComponents before. The code snippets are shown below:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import java.io.File;
import java.io.PrintWriter;
import java.io.IOException;
import java.io.FileNotFoundException;
import java.awt.image.BufferedImage;
import javax.imageio.ImageIO;
import java.util.Scanner;

public class Hello extends JPanel implements KeyListener, MouseListener{
    JPanel panel = new JPanel();
    JFrame frame = new JFrame();
    public Hello(){
        addKeyListener(this);
        addMouseListener(this);
    }
    public static void main(String [] args){
        Hello play = new Hello();
        play.setPanel();
    }
    public void setPanel(){
        panel.setLayout(null);
        frame.add(panel);
        frame.setLayout(null);
        panel.setBounds(0,0,100,100);
        frame.setVisible(true);
        panel.setVisible(true);
        panel.setFocusable(true);
        frame.setSize(100,100);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
    public void keyTyped(KeyEvent evt){
        System.out.println("keytyped");
    }
    public void keyPressed(KeyEvent evt){
        System.out.print("keypressed");
    }
    public void keyReleased(KeyEvent evt){
        System.out.println("keyreleased");
    }
    public void mousePressed(MouseEvent evt){
        System.out.println("mousepressed");
    }
    public void mouseReleased(MouseEvent evt){
        System.out.println("mousereleased");
    }
    public void mouseClicked(MouseEvent evt){
        System.out.println("mouseclicked");
    }
    public void mouseEntered(MouseEvent evt){
        System.out.println("mousenentered");
    }
    public void mouseExited(MouseEvent evt){
        System.out.println("mouseexited");
    }
}

Off topic: I keep getting the error Your post appears to contain code that is not properly formatted as code. Please indent all code by 4 spaces using the code toolbar button or the CTRL+K keyboard shortcut. For more editing help, click the [?] toolbar icon. I have no idea how to fix it. Sometimes I put everything in code and it still won't submit.

Sean Connolly

Have a look at Java KeyListener for JFrame is being unresponsive?.

You need to register your KeyListener and MouseListener for every JComponent you want to listen to:

public Hello() {
    addKeyListener(this);
    addMouseListener(this);
    panel.addKeyListener(this);
    panel.addMouseListener(this);
    frame.addKeyListener(this);
    frame.addMouseListener(this);
}

Edit:
Key and mouse events are only fired from the JComponent which has focus at the time. Because of this there seems to be a consensus that KeyBindings may be favorable to KeyListeners. The two have their applications, however, and so there is no hard and fast rule here. Have a read of 'How to Write a Key Listener' and 'How to Write a Key Binding' and you'll get the gist.

Better to avoid using KeyListeners with JPanel, use KeyBindings instead. JPanel cannot gain focus so cannot interact with KeyEvents. Using KeyBindings, you can map an Action to a KeyStroke even when a component doesn't have focus.

Try this instead:

 panel.addKeyListener(this);
 panel.addMouseListener(this);

You have to add the listeners to every component you want to listen to.

来源：https://stackoverflow.com/questions/14085757/mouselistener-keylistener-not-working-jpanel

标签

java

swing

jpanel

keylistener

mouselistener