how do you add a key listener to a java GUI?
can anyone pls show me how...
or at least give an example..pls:)

cause I want to add a key listener to my GUI calculator
but I don't now how or where to put it and stuff...:-/

thanks...

my key listener is on the last part...and i don't know what to do with it...
i'm suppose to add a key listener to this code...

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

import java.awt.event.KeyEvent;




class CalcGUI extends JPanel {


    //=============================================== instance variables
    //--- variable for GUI elements
    private JTextField _displayField;        // display result / input.
    //--- variables representing state of the calculator
    private boolean    _startNumber = true;  // true: num key next
    private double        _resultValue = 0.0;     // result so far
    private String     _previousOp  = "=";   // previous operation
    //end instance variables

    //-------------------------------------------- static (class) variables
    private static final Font BIGGER_FONT = new Font("monspaced",
 Font.PLAIN, 24);


    //======================================================constructor
    public CalcGUI() {
        //--- Display field
        _displayField = new JTextField("0", 12);
        _displayField.setHorizontalAlignment(JTextField.RIGHT);
        _displayField.setFont(BIGGER_FONT);


        //--- Clear button
        JButton clearButton = new JButton("CLEAR");
        clearButton.setFont(BIGGER_FONT);
        clearButton.addActionListener(
            new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    action_clear();
                }
            }
        );

        //--- Use one listener for all numeric keys.
        ActionListener numListener =
            new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    action_num(e);  // process it below
                }
            };

        //--- Layout numeric keys in a grid.
        //--- Use the characters in a string as a guide
        //--- for producing the numeric keys.
        String buttonOrder = "789456123 0 ";
        JPanel buttonPanel = new JPanel(new GridLayout(5, 3));
        for (int i = 0; i < buttonOrder.length(); i++) {
            String keyTop = buttonOrder.substring(i, i+1);
            if (keyTop.equals(" ")) {
                buttonPanel.add(new JLabel(""));
            } else {
                JButton b = new JButton(keyTop);
                b.addActionListener(numListener);
                b.setFont(BIGGER_FONT);
                buttonPanel.add(b);
            }
        }

        //--- Create an ActionListener that will be used for
        //--- all of the operator buttons.
        ActionListener opListener =
            new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                   action_op(e);
                }//endmethod actionPerformed
           };


        //--- Create panel with gridlayout to hold operator buttons.
        //--- Use array of button names to create buttons in a loop.
        JPanel opPanel = new JPanel(new GridLayout(5, 1));
        String[] opOrder = {"+", "-", "*", "/", "=","%"};
        for (int i = 0; i < opOrder.length; i++) {
            JButton b = new JButton(opOrder[i]);
            b.addActionListener(opListener);
            b.setFont(BIGGER_FONT);
            opPanel.add(b);
            }
            JButton c= new JButton(".");
            c.setFont(BIGGER_FONT);
            opPanel.add(c);

        /**c.addKeyListener( new KeyListener (){
                public void keyPressed( KeyEvent e){
                    _displayField.setText(".");
                }
                });*/




        //--- Layout this, the top level, panel.
        this.setLayout(new BorderLayout());
        this.add(_displayField, BorderLayout.NORTH );
        this.add(buttonPanel  , BorderLayout.CENTER);
        this.add(opPanel      , BorderLayout.EAST  );
        this.add(clearButton  , BorderLayout.SOUTH );
         this.add(MyPanel, BorderLayout.SOUTH);     
    }//end constructor


    //============================================================ action_op
    // Called by the action listener for all op buttons.
    private void action_op(ActionEvent e) {
        // The calculator is always in one of two states.
        // 1. A number must be entered next (so this operator is wrong).
        // 2. An operator must be entered next (so we're ok).
        if (_startNumber) { // Error: needed number, not operator
            action_clear();
            _displayField.setText("ERROR");
        } else {
            _startNumber = true;  // Next thing must be a number
            try {
                // Get the value from display field, convert it, do prev op
                // If this is the first op, _previousOp will be =.
                int currentValue =
 Integer.parseInt(_displayField.getText());
                double currentValuez = Double.parseDouble(_displayField.getText());
                //int d=Integer.parseInt(c);

                if (_previousOp.equals("=")) {
                    _resultValue = currentValue;
                } else if (_previousOp.equals("+")) {
                    _resultValue += currentValuez;
                } else if (_previousOp.equals("-")) {
                    _resultValue -= currentValuez;
                } else if (_previousOp.equals("*")) {
                    _resultValue *= currentValuez;
                } else if (_previousOp.equals("/")) {
                    _resultValue /= currentValue;
                } else if (_previousOp.equals("%")) {
                    _resultValue %= currentValue;
                }

                _displayField.setText(""+_resultValue);

            } catch (NumberFormatException ex) {
                action_clear();
                _displayField.setText("Error");
            }

            //--- set _previousOp for the next operator.
            _previousOp = e.getActionCommand();
        }//endif _startNumber
    }//endmethod action_op


    //======================================================== action_num
    // Called by the action listener for numeric keys
    private void action_num(ActionEvent e) {
        String digit = e.getActionCommand(); // gets text from digitkey
        if (_startNumber) {
            // This is the first digit, clear field and set
            _displayField.setText(digit);
            _startNumber = false;
        } else {
            // Add this digit to the end of the display field
            _displayField.setText(_displayField.getText() + digit);
        }
    }//endmethod action_num


    //=============================================== logic action_clear
    // Called by the action listener for the Clear button
    public void action_clear() {
        _startNumber = true;
        _displayField.setText("0");
        _resultValue = 0.0;
        _previousOp  = "=";




    }//endmethod action_clear

}//endclass CalcGUI

class MyPanel extends JPanel implements KeyListener{

    public MyPanel(){
        this.setFocusable(true);
        this.addKeyListener(this);
    }

    public void keyTyped(KeyEvent e){
         char i = e.getKeyChar();
         System.out.println("Key Typed: " + i);
    }

    public void keyPressed(KeyEvent e){
         char i = e.getKeyChar();
         System.out.println("Key Pressed: " + i);
    }
    public void keyReleased(KeyEvent e){
         char i = e.getKeyChar();
         System.out.println("Key Released: " + i);
    }
}

Edited 3 Years Ago by mike_2000_17: Fixed formatting

Why does your listener need to extend JPanel? Your class can just implement KeyListener or extend KeyAdapter and be added to a component with the .addKeyListener( new MyListener() ) call. When a key is pressed in that component, the listener will fire and you process it accordingly.

Đầu tiên cho Focus cái JPanel rùi cho nó lắng nghe KeyListener trên chínhd nó là OK.

this.setFocusable(true);
this.addKeyListener((KeyListener)this);

package AppKeyListener;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class MyPanel extends JPanel implements KeyListener {
    public MyPanel(){
        super();
        this.setBackground(Color.gray);
        this.setFocusable(true);  
        this.addKeyListener((KeyListener)this);
    }
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(color);
        g.fillRect(x, y, 100, 50);
    }
    int x=100,y=50;
    Color color=Color.red;
    
// Main method

    public static void main(String[] args) {
        // TODO code application logic here
        JFrame frm =new JFrame("App Key Listener");
        frm.setSize(400, 300);
        frm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frm.setVisible(true);
        MyPanel p =new MyPanel();
        frm.add(p);        
    }
    public void keyTyped(KeyEvent e) {
        //throw new UnsupportedOperationException("Not supported yet.");
    }

    public void keyPressed(KeyEvent e) {
        if(e.getKeyChar()=='g')
            color=Color.GREEN;
        if(e.getKeyChar()=='r')
            color=Color.red;
        if(e.getKeyChar()=='b')
            color=Color.blue;
        if(e.getKeyChar()=='y')
            color=Color.yellow;
        if(e.getKeyChar()=='w')
            color=Color.WHITE;
        if(e.getKeyCode()==KeyEvent.VK_UP)
            y-=2;
        if(e.getKeyCode()==KeyEvent.VK_DOWN)
            y+=2;
        if(e.getKeyCode()==KeyEvent.VK_RIGHT)
            x+=2;
        if(e.getKeyCode()==KeyEvent.VK_LEFT)
            x-=2;
        this.repaint();
    }
    public void keyReleased(KeyEvent e) {
        //throw new UnsupportedOperationException("Not supported yet.");
    }
}

Add KeyListener on Jpanel:

Focus JPanel and add KeyListener on its. OK.hjhj

this.setFocusable(true);
this.addKeyListener((KeyListener)this);

package AppKeyListener;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class MyPanel extends JPanel implements KeyListener {
    public MyPanel(){
        super();
        this.setBackground(Color.gray);
        this.setFocusable(true);  
        this.addKeyListener((KeyListener)this);
    }
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(color);
        g.fillRect(x, y, 100, 50);
    }
    int x=100,y=50;
    Color color=Color.red;
    
// Main method

    public static void main(String[] args) {
        // TODO code application logic here
        JFrame frm =new JFrame("App Key Listener");
        frm.setSize(400, 300);
        frm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frm.setVisible(true);
        MyPanel p =new MyPanel();
        frm.add(p);        
    }
    public void keyTyped(KeyEvent e) {
        //throw new UnsupportedOperationException("Not supported yet.");
    }

    public void keyPressed(KeyEvent e) {
        if(e.getKeyChar()=='g')
            color=Color.GREEN;
        if(e.getKeyChar()=='r')
            color=Color.red;
        if(e.getKeyChar()=='b')
            color=Color.blue;
        if(e.getKeyChar()=='y')
            color=Color.yellow;
        if(e.getKeyChar()=='w')
            color=Color.WHITE;
        if(e.getKeyCode()==KeyEvent.VK_UP)
            y-=2;
        if(e.getKeyCode()==KeyEvent.VK_DOWN)
            y+=2;
        if(e.getKeyCode()==KeyEvent.VK_RIGHT)
            x+=2;
        if(e.getKeyCode()==KeyEvent.VK_LEFT)
            x-=2;
        this.repaint();
    }
    public void keyReleased(KeyEvent e) {
        //throw new UnsupportedOperationException("Not supported yet.");
    }
}

Edited 7 Years Ago by phamvantu_ctk30: n/a

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