Event-Driven Programming

Question

Hello Everyone,
I am new to this forum and also new to event-driven programming. Anyways, I am doing a small exercise to get myself familiar with event-driven programming. In particular, the program responds to keys entered on a keyboard. The exercise in a way resembles how a second hand moves in a clock. So, here's what I am trying to do. Originally the hand points at 12 o'clock. when I press the right arrow key the hand should move 6 degrees to the right and when I press the left arrow key the hand should move 6 degrees to the left. The code I have so far seems fairly correct to me but when I run the program and press the arrow keys on my keyboard nothing happens. Any help would be appreciated and thank you in advance.
Here is my code:
import java.awt.*;
import java.util.*;
import java.awt.event.*;
import javax.swing.*;
public class hittingBalloons extends JFrame{
     hittingBalloons(){
          mouseKeyboardListeners p = new mouseKeyboardListeners();
          add(p);
          p.setFocusable(true);
     public static void main(String[] args){
          hittingBalloons frame = new hittingBalloons();
          frame.setTitle("Hitting Balloons");
          frame.setSize(500,500);
          frame.setLocationRelativeTo(null);
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          frame.setVisible(true);
     public class mouseKeyboardListeners extends JPanel{
          private int xCenter=250;
          private int yCenter=250;
          private int xEnd =250;
          private int yEnd =210;
          private int angle=0;
          private int gunLength=40;
          private int xBall = 150;
          private int yBall = 150;
          private int radius = 20;
          public mouseKeyboardListeners(){
               addKeyListener(new KeyAdapter(){
                    public void keyPressed(KeyEvent e){
                         if(e.getKeyCode() == KeyEvent.VK_LEFT){
                              angle = (int)(angle - (Math.PI/30));
                              xEnd = (int)(xCenter + gunLength*Math.sin(angle));
                              yEnd = (int)(yCenter - gunLength*Math.cos(angle));
                              repaint();
                         else if (e.getKeyCode() == KeyEvent.VK_RIGHT){
                              angle = (int)(angle + (Math.PI/30));
                              xEnd = (int)(xCenter + gunLength*Math.sin(angle));
                              yEnd = (int)(yCenter - gunLength*Math.cos(angle));
                              repaint();
          protected void paintComponent(Graphics g){
               super.paintComponent(g);
               g.drawLine(xCenter,yCenter,xEnd,yEnd);
}

Answer 1

A few notes and suggestions:
1) Welcome to the forum!
2) When posting code, please use code tags as it makes your code easier to read. the FAQ will show you how. e.g.,
import java.awt.*;
import java.util.*;
import java.awt.event.*;
import javax.swing.*;
public class hittingBalloons extends JFrame{
     hittingBalloons(){
          mouseKeyboardListeners p = new mouseKeyboardListeners();
          add(p);
          p.setFocusable(true);
     public static void main(String[] args){
          hittingBalloons frame = new hittingBalloons();
          frame.setTitle("Hitting Balloons");
          frame.setSize(500,500);
          frame.setLocationRelativeTo(null);
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          frame.setVisible(true);
     public class mouseKeyboardListeners extends JPanel{
          private int xCenter=250;
          private int yCenter=250;
          private int xEnd =250;
          private int yEnd =210;
          private int angle=0;
          private int gunLength=40;
          private int xBall = 150;
          private int yBall = 150;
          private int radius = 20;
          public  mouseKeyboardListeners(){
               addKeyListener(new KeyAdapter(){
                    public void keyPressed(KeyEvent e){
                         if(e.getKeyCode() == KeyEvent.VK_LEFT){
                              angle = (int)(angle - (Math.PI/30));
                              xEnd = (int)(xCenter + gunLength*Math.sin(angle));
                              yEnd = (int)(yCenter - gunLength*Math.cos(angle));
                              repaint();
                         else if (e.getKeyCode() == KeyEvent.VK_RIGHT){
                              angle = (int)(angle + (Math.PI/30));
                              xEnd = (int)(xCenter + gunLength*Math.sin(angle));
                              yEnd = (int)(yCenter - gunLength*Math.cos(angle));
                              repaint();
          protected void paintComponent(Graphics g){
               super.paintComponent(g);
               g.drawLine(xCenter,yCenter,xEnd,yEnd);
}3) For key listeners to work, the component must have the focus, and JPanels don't get focus by default. You have to call setFocusable(true) first and then request focus in window on the JPanel.
4) Even better would be to use key binding, and to learn to use these, check out the Sun tutorial.
Luck and again, welcome!