Develop Reference

ActionListener and KeyListener Error

I am making a class (called Play), that extends JFrame, and implements ActionListener and KeyListener. This class does not hold the main() method, because there is a different class for that.
I am getting an error which states, "Class Play must either be declared abstract, or implement abstract method keyReleased(KeyEvent) in KeyListener".
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.geom.Ellipse2D;
public class Play extends JFrame implements ActionListener, KeyListener {
Timer timer = new Timer(5, this);
double x = 0, y = 0, velx = 0, vely = 0;
public Play() {
timer.start();
addKeyListener(this);
setFocusable(true);
setFocusTraversalKeysEnabled(false);
}
public void paint(Graphics g) {
super.paint(g);
Graphics2D g2 = (Graphics2D) g;
g2.fill(new Ellipse2D.Double(x, y, 40, 40));
}
public void actionPreformed(ActionEvent e) {
repaint();
x += velx;
y += vely;
}
public void up() {
vely = -1.5;
velx = 0;
}
public void down() {
vely = 1.5;
velx = 0;
}
public void left() {
vely = 0;
velx = -1.5;
}
public void right() {
vely = 0;
velx = 1.5;
}
public void keyPressed(KeyEvent e) {
int code = e.getKeyCode();
if (code == KeyEvent.VK_UP) {
up();
}
if (code == KeyEvent.VK_DOWN) {
down();
}
if (code == KeyEvent.VK_LEFT) {
left();
}
if (code == KeyEvent.VK_RIGHT) {
right();
}
}
public void keyReleased(KeyEvent e) {
}
public void keyTyped(KeyEvent e) {
}
}

Well, do what it says. Since you're inheriting the KeyListener interface, you have to implement all of the interface's methods, including 'keyReleased'

The KeyListener must have all of it's methods implemented.
Simply add this method to the class and it should work
#Override
public void keyReleased(KeyEvent e) {
}
You must also Override all of the KeyListener implemented methods

Eclipse vs BlueJ issue

I tried this code in BlueJ which should create a rectangle and move it around but it does not function. Then I put the same exact code into Eclipse and it functions as I thought it would. Any ideas to why this works in Eclipse but not in BlueJ?
import javax.swing.*;
import java.awt.*;
public class Shapes
{
public static void main(String[] args)
{
JFrame frame = new JFrame("Test");
Draw object = new Draw();
frame.add(object);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(400,400);
frame.setVisible(true);
}
}
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Draw extends JPanel implements ActionListener, KeyListener
{
Timer tm = new Timer(5,this);
int x = 0, y = 0, velX = 0, velY = 0;
public Draw()
{
tm.start();
addKeyListener(this);
setFocusable(true);
setFocusTraversalKeysEnabled(false);
}
public void paintComponent(Graphics g)
{
super.paintComponent(g);
g.setColor(Color.BLUE);
g.fillRect(x,y,100,20);
}
public void actionPerformed(ActionEvent e)
{
x += velX;
y += velY;
repaint();
}
public void keyPressed(KeyEvent e)
{
int c = e.getKeyCode();
if(c == KeyEvent.VK_LEFT)
{
velX = -1;
velY = 0;
}
if(c == KeyEvent.VK_UP)
{
velX = 0;
velY = 1;
}
if(c == KeyEvent.VK_RIGHT)
{
velX = 1;
velY = 0;
}
if(c == KeyEvent.VK_DOWN)
{
velX = 0;
velY = -1;
}
}
public void keyTyped(KeyEvent e){}
public void keyReleased(KeyEvent e)
{
velX = 0;
velY = 0;
}
}

I can see what you mean I believe it attaches it to that corner of the screen because when I resize the screen it moves with that corner. I think its not that BlueJ can't Run it properly i believe it can but it does it differently than what eclipse does.
I believe this question asks the same thing and it gets pretty good answers you should look at it first.

Image location does not change in response to key events

package testapplication;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
public class TestApplication extends JFrame implements Runnable {
int sizex = 800;
int sizey = 650;
int x, y, xDirection, yDirection;
private Image dbImage;
private Graphics dbg;
Image character;
#Override
public void run(){
try{
while(true){
move();
Thread.sleep(5);
}
}
catch(Exception e){
System.out.println("ERROR!!!");
}
}
public void move(){
x += xDirection;
y += yDirection;
if(x <= 0)
x = 0;
if(x >= 778)
x = 778;
if(y <= 22)
y = 22;
if(y >= 628)
y = 628;
}
public void setXDirection(int xdir){
xDirection = xdir;
}
public void setYDirection(int ydir){
yDirection = ydir;
}
Font font = new Font("Arial", Font.BOLD, 30);
public class AL extends KeyAdapter {
#Override
public void keyPressed(KeyEvent e) {
int keyCode = e.getKeyCode();
//Key press inputs "WASD"
if(keyCode == KeyEvent.VK_W) {
setYDirection(-1);
}
if(keyCode == KeyEvent.VK_A) {
setXDirection(-1);
}
if(keyCode == KeyEvent.VK_S) {
setYDirection(+1);
}
if(keyCode == KeyEvent.VK_D) {
setXDirection(+1);
}
//end Key press inputs "WASD"
}
#Override
public void keyReleased(KeyEvent e) {
int keyCode = e.getKeyCode();
//Key release inputs "WASD"
if(keyCode == KeyEvent.VK_W) {
setYDirection(0);
}
if(keyCode == KeyEvent.VK_A) {
setXDirection(0);
}
if(keyCode == KeyEvent.VK_S) {
setYDirection(0);
}
if(keyCode == KeyEvent.VK_D) {
setXDirection(0);
}
//end Key release inputs "WASD"
}
}
public TestApplication() {
//Load images
ImageIcon i = new ImageIcon("C:/Users/Min/Documents/NetBeansProjects/TestApplication/src/testapplication/Untitled-1.png") {};
character = i.getImage();
//Game properties
addKeyListener(new AL());
setTitle("TestApplication");
setSize(sizex, sizey);
setResizable(false);
setVisible(true);
setBackground(Color.LIGHT_GRAY);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
x = 30;
y = 628;
}
#Override
public void paint(Graphics g) {
dbImage = createImage(getWidth(), getHeight());
dbg = dbImage.getGraphics();
paintComponent(dbg);
g.drawImage(dbImage, 0, 0, this);
}
public void paintComponent(Graphics g) {
g.setFont(font);
g.setColor(Color.RED);
g.drawString("Welcome to TESTTEST", 300,125);
g.setColor(Color.RED);
g.drawImage(character, x, y, this);
repaint();
}
public static void main(String[] args) {
TestApplication ta = new TestApplication();
//Threads
Thread t1 = new Thread();
t1.start();
}
}
In my Java code, there is supposed to be an image that moves using the WASD keys. The image shows, yet it will not move. What's wrong?
This is a simple Java code that is supposed to make an image roam around the window with WASD keys. I am not sure what I did wrong in the code, I've double checked and everything looked fine...

First of all, if you need to change the image location while the user presses one of the wsda keys then you need to add 1 and -1 to the current value of x and y ( image location). You just set 1 and -1 which will move the image just one pixel even if, for example, you press the d button multiple times over and over.
You need to change method setXDirection to this (I have added a plus before the equal sign to add xDir value to whatever xDirection is.)
public void setXDirection(int xDir)
{
xDirection += xDir
}
Make the same correction with yDirection (yDirection += yDir)
Second, you don't call your paint method. You have to call it each time your user presses a key (one of wasd ofcourse), so do it at the final line of your keyReleased method.
I hope these two correct your code but I think you need to recheck the code again with much care.
Good luck,
Iman

You forgot to add the Runnable instance to the Thread constructor.
Your main method should be:
public static void main(String[] args) {
TestApplication ta = new TestApplication();
//Threads
Thread t1 = new Thread(ta);
t1.start();
}

One class over riding the second one?

I wrote a Java program that has 3 classes:
main.class (main method class)
Infout.class (class that draws circle + methods for circle that allow it to be controlled with keyboard input (arrow keys)
obj2.class (class that draws a rectangle)
All the code is compiled fine, but for some reason when I run the program, the program executes all the code from obj2.class but does not execute the one from Infout.class.
In other words, it draws the rectangle (obj2.class) but it does not draw the controllable circle (Infout.class). Is Obj2.class over riding Infout.class? If it is, what should I do?
The code is much too big to post here, the website says the post is "mostly code" :c.
Thanks!
EDIT: Ok here's the relevant code:
main.class
import javax.swing.JFrame;
public class main {
public static void main(String args[]) {
JFrame frame = new JFrame();
Infout m = new Infout();
obj2 o = new obj2();
frame.add(m);
frame.add(o);
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(300, 400);
frame.setTitle("Circle");
}
}
Infout.class
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
public class Infout extends JPanel implements ActionListener, KeyListener {
Timer t = new Timer(5, this);
double x = 0, y = 0, velx = 0, vely = 0;
public Infout(){
t.start();
addKeyListener(this);
setFocusable(true);
setFocusTraversalKeysEnabled(false);
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.fill(new Ellipse2D.Double(x, y, 40, 40));
}
public void actionPerformed(ActionEvent e) {
repaint();
x += velx;
y += vely;
if (x < 0 || x > 260)
{
velx = 0;
vely = 0;
}
if (y < 0 || y > 340)
{
velx = 0;
vely = 0;
}
}
public void up() {
vely = -1.5;
velx = 0;
}
public void down() {
vely = 1.5;
velx = 0;
}
public void left() {
velx = -1.5;
vely = 0;
}
public void right() {
velx = 1.5;
vely = 0;
}
public void keyPressed(KeyEvent e) {
int code = e.getKeyCode();
if (code == KeyEvent.VK_UP) {
up();
}
if (code == KeyEvent.VK_DOWN) {
down();
}
if (code == KeyEvent.VK_RIGHT) {
right();
}
if (code == KeyEvent.VK_LEFT) {
left();
}
}
public void keyTyped(KeyEvent e) {}
public void keyReleased(KeyEvent e) {}
}
obj2.class
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Ellipse2D;
import javax.swing.JPanel;
public class obj2 extends JPanel{
int x;
int y;
public obj2(){
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.fill(new Ellipse2D.Double(10, 20, 40, 40));
}
}

Infout and obj2 are not related.
Because obj2 extends JPanel, the call super.paintComponent(g) calls JPanel's version. If you obj2 to be a subclass of Infout, then you need to use extends:
public class obj2 extends Infout {
// Code here
}
Once this is done, super will refer to Infout.

Detect overlapping objects in java Swing

I am trying to make a program that has a moving ball and a platform that it will sit on. I am new too java and I cant figure out how to detect when 2 swing objects are overlapping. My code it below and I am wondering what the best way is to detect overlapping objects.
KeyDemo.java:
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class KeyDemo
{
public static void main(String[] args)
{
JFrame frame = new JFrame();
JPanel panel = new JPanel();
LayoutManager overlay = new OverlayLayout(panel);
panel.setLayout(overlay);
final int FRAME_WIDTH = 800;
final int FRAME_HEIGHT = 600;
frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
frame.setTitle("Move the Ball");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
final WallComponent wc1 = new WallComponent(400, 400);
final BallComponent bc = new BallComponent(400, 300);
panel.add(wc1);
panel.add(bc);
frame.add(panel);
KeyboardController kc = new KeyboardController(bc);
frame.addKeyListener(kc);
frame.setVisible(true);
class AnimationListener implements ActionListener{
public void actionPerformed(ActionEvent event){
bc.tick();
//wc1.checkOverlap(bc);
}
}
ActionListener aListener = new AnimationListener();
final Timer timer = new Timer(1, aListener);
timer.start();
}
}
KeyboardController.java:
import java.awt.*;
import java.awt.event.*;
public class KeyboardController implements KeyListener
{
BallComponent bComp;
public KeyboardController(BallComponent t)
{
bComp = t;
}
/** Handle the key pressed event from the text field. */
public void keyPressed(KeyEvent e) {
int keyCode = e.getKeyCode();
if(keyCode == 38)
{
System.out.println("Pressed Up!");
bComp.moveUp();
}
if(keyCode == 37)
{
System.out.println("Pressed Left!");
bComp.moveLeft();
}
if(keyCode == 39)
{
System.out.println("Pressed Right!");
bComp.moveRight();
}
if(keyCode == 40)
{
System.out.println("Pressed Down!");
bComp.moveDown();
}
}
/** Handle the key released event from the text field. */
public void keyReleased(KeyEvent e) {
int keyCode = e.getKeyCode();
if(keyCode == 38)
{
System.out.println("Released Up!");
bComp.stopY();
}
if(keyCode == 37)
{
System.out.println("Released Left!");
bComp.stopX();
}
if(keyCode == 39)
{
System.out.println("Released Right!");
bComp.stopX();
}
if(keyCode == 40)
{
System.out.println("Pressed Down!");
bComp.stopY();
}
}
public void keyTyped(KeyEvent e) {
}
}
BallComponent.java:
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
public class BallComponent extends JComponent
{
int xSpeed;
int ySpeed;
int x;
int y;
public BallComponent(int x, int y)
{
super();
this.x = x;
this.y = y;
}
public void paintComponent(Graphics g)
{
Graphics2D g2 = (Graphics2D)g;
Ellipse2D.Double ball = new Ellipse2D.Double(x-10,y-10,10,10);
g2.setColor(Color.RED);
g2.fill(ball);
g2.draw(ball);
}
public void moveLeft()
{
xSpeed=-1;
}
public void moveRight()
{
xSpeed=1;
}
public void moveUp()
{
ySpeed=-1;
}
public void moveDown()
{
ySpeed=1;
}
public void tick()
{
x=x+xSpeed;
y=y+ySpeed;
repaint();
}
public void stopY()
{
ySpeed=0;
}
public void stopX()
{
xSpeed=0;
}
}
WallComponent.java:
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
public class WallComponent extends JComponent
{
int x;
int y;
public WallComponent(int x, int y)
{
super();
this.x = x;
this.y = y;
}
public void paintComponent(Graphics g)
{
Graphics2D g2 = (Graphics2D)g;
Rectangle wall = new Rectangle(x-40,y-40,40,40);
g2.setColor(Color.YELLOW);
g2.fill(wall);
g2.draw(wall);
}
public void checkOverlap(BallComponent bc){
if (this.contains(bc.getLocation())){
bc.stopY();
bc.stopX();
}
}
}

All Swing components have a concept of "bounds". This is a rectangular area within which they are "drawn".
If you are controlling the size and position correctly, you should be able to use the contains method of the Rectangle which is returned from calling Component#getBounds
So you checkOverlap method could look like...
public void checkOverlap(BallComponent bc){
if (getBounds().intersects(bc.getBounds())){
bc.stopY();
bc.stopX();
}
}
You will also want to make sure that you are calling super.paintComponent before performing any custom painting, espeically when using components that extend from JComponent. This will ensure that the Graphics context is prepared for painting correctly...
Updated
There's a cascade of issues. Basically, instead of positing the components within the parent container yourself (which is how I thought you had done it), you've laid each component out to fill the parent container and only "painted" the objects...This makes life more difficult
Instead, if you are going to use components, I would use a null layout (or even possibly use a JLayeredPane as the parent container).
I would then change the physical position of the components, for example...
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.LayoutManager;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.geom.Ellipse2D;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.OverlayLayout;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class TestGame {
public static void main(String[] args) {
new TestGame();
}
public TestGame() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
}
JFrame frame = new JFrame();
JPanel panel = new JPanel();
panel.setLayout(null);
final int FRAME_WIDTH = 800;
final int FRAME_HEIGHT = 600;
frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
frame.setTitle("Move the Ball");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
final WallComponent wc1 = new WallComponent(400, 400);
final BallComponent bc = new BallComponent(400, 300);
panel.add(wc1);
panel.add(bc);
frame.add(panel);
KeyboardController kc = new KeyboardController(bc);
frame.addKeyListener(kc);
frame.setVisible(true);
class AnimationListener implements ActionListener {
public void actionPerformed(ActionEvent event) {
bc.tick();
wc1.checkOverlap(bc);
}
}
ActionListener aListener = new AnimationListener();
final Timer timer = new Timer(1, aListener);
timer.start();
}
});
}
public class KeyboardController implements KeyListener {
BallComponent bComp;
public KeyboardController(BallComponent t) {
bComp = t;
}
/**
* Handle the key pressed event from the text field.
*/
public void keyPressed(KeyEvent e) {
int keyCode = e.getKeyCode();
if (keyCode == 38) {
System.out.println("Pressed Up!");
bComp.moveUp();
}
if (keyCode == 37) {
System.out.println("Pressed Left!");
bComp.moveLeft();
}
if (keyCode == 39) {
System.out.println("Pressed Right!");
bComp.moveRight();
}
if (keyCode == 40) {
System.out.println("Pressed Down!");
bComp.moveDown();
}
}
/**
* Handle the key released event from the text field.
*/
public void keyReleased(KeyEvent e) {
int keyCode = e.getKeyCode();
if (keyCode == 38) {
System.out.println("Released Up!");
bComp.stopY();
}
if (keyCode == 37) {
System.out.println("Released Left!");
bComp.stopX();
}
if (keyCode == 39) {
System.out.println("Released Right!");
bComp.stopX();
}
if (keyCode == 40) {
System.out.println("Pressed Down!");
bComp.stopY();
}
}
public void keyTyped(KeyEvent e) {
}
}
public class BallComponent extends JComponent {
int xSpeed;
int ySpeed;
public BallComponent(int x, int y) {
super();
setBounds(x, y, 10, 10);
}
public void paintComponent(Graphics g) {
Graphics2D g2 = (Graphics2D) g;
Ellipse2D.Double ball = new Ellipse2D.Double(0, 0, 9, 9);
g2.setColor(Color.RED);
g2.fill(ball);
g2.draw(ball);
}
public void moveLeft() {
xSpeed = -1;
}
public void moveRight() {
xSpeed = 1;
}
public void moveUp() {
ySpeed = -1;
}
public void moveDown() {
ySpeed = 1;
}
public void tick() {
int x = getX() + xSpeed;
int y = getY() + ySpeed;
setLocation(x, y);
repaint();
}
public void stopY() {
ySpeed = 0;
}
public void stopX() {
xSpeed = 0;
}
}
public class WallComponent extends JComponent {
public WallComponent(int x, int y) {
super();
setBounds(x, y, 40, 40);
}
public void paintComponent(Graphics g) {
Graphics2D g2 = (Graphics2D) g;
Rectangle wall = new Rectangle(0, 0, 40, 40);
g2.setColor(Color.YELLOW);
g2.fill(wall);
g2.draw(wall);
}
public void checkOverlap(BallComponent bc) {
System.out.println(" me: " + getBounds());
System.out.println("you: " + bc.getBounds());
if (getBounds().intersects(bc.getBounds())) {
bc.stopY();
bc.stopX();
}
}
}
}
Now, you could use "painted" objects, but in that case I would have a virtual concept of a Ball and Wall which you could paint within a single component. These objects would need to provide information about there position and size, which you could, again, check using Rectangle#intersects...

Generally, just try to make a "bounding box" for your objects. This will be the invisible rectangle that goes with the object. Then just do
if(rectangle1.intersects(rectangle2)) ...
The intersects method only works with rectangles, and that's why you need a bounding box.