Develop Reference

How to make Java game more efficient?

I have been working on a flappy bird clone so I can get more practice programming. Everything in the game works, however the game has frame skips and lag drops, and I do not know how to make Java programs run more smoothly. Am I supposed to measure the amount of time a method takes and try to shorten that, or do I do something else? I have seen people explain how to program Java games, but there is hardly anything on improving the performance. Any advice would be helpful. Thank you.
Hazards class
package entity;
import java.util.ArrayList;
public class Hazards {
public ArrayList<Horizontal> hors;
public ArrayList<Vertical> verts;
public Hazards(int width, int height, int thickness) {
hors = new ArrayList<Horizontal>();
hors.add(new Horizontal(0, 0, width, thickness));
hors.add(new Horizontal(0, height-thickness, width, thickness));
verts = new ArrayList<Vertical>();
}
}
Horizontal class
package entity;
import java.awt.Rectangle;
public class Horizontal {
public int xPos, yPos, width, height;
public Rectangle bounds;
public Horizontal(int x, int y, int w, int h) {
this.xPos = x;
this.yPos = y;
this.width = w;
this.height = h;
this.bounds = new Rectangle(x, y, w, h);
}
public void updateBounds(int x, int y, int w, int h) {
this.xPos = x;
this.yPos = y;
this.width = w;
this.height = h;
this.bounds = new Rectangle(x, y, w, h);
}
}
Vertical class
package entity;
import java.awt.Rectangle;
import java.util.Random;
public class Vertical {
public int xPos, width, gapSize, gapPos;
public boolean scoredOn = false;
public Rectangle top, bottom;
public Vertical(int xPos, int width, int roofHeight, int floorHeight, int gapSize) {
this.xPos = xPos;
this.width = width;
this.gapPos = new Random().nextInt(floorHeight - gapSize) + roofHeight;
this.top = new Rectangle();
this.bottom = new Rectangle();
this.top.setBounds(xPos, 0, width, gapPos);
this.bottom.setBounds(xPos, gapPos + gapSize, width, floorHeight - roofHeight + top.height + gapSize);
}
}
Content class
package main;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Rectangle;
import javax.swing.JPanel;
public class Content extends JPanel {
private static final long serialVersionUID = 1L;
private Engine e;
private Rectangle bounds;
public Content(Engine engine) {
e = engine;
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.clearRect(0, 0, this.getWidth(), this.getHeight());
// Roof and floor
g.setColor(Color.black);
for (int x = 0; x < e.e.hors.size(); x++) {
bounds = e.e.hors.get(x).bounds;
g.fillRect(bounds.x, bounds.y, bounds.width, bounds.height);
}
// Pipes
g.setColor(Color.black);
for(int x = 0; x < e.e.verts.size(); x++) {
bounds = e.e.verts.get(x).top;
g.fillRect(bounds.x, bounds.y, bounds.width, bounds.height);
bounds = e.e.verts.get(x).bottom;
g.fillRect(bounds.x, bounds.y, bounds.width, bounds.height);
}
// Player
g.setColor(Color.black);
g.fillRect((int) e.p.xPos, (int) e.p.yPos, e.p.size, e.p.size);
// Score
g.setColor(Color.blue);
g.setFont(new Font("Monospaced", Font.PLAIN, 40));
g.drawString(Integer.toString(e.p.score), e.width/2, 80);
}
}
Engine class
package main;
import java.awt.Dimension;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import entity.Hazards;
import entity.Vertical;
import screen.TitleScreen;
public class Engine implements Runnable {
public JFrame f;
public String title = "Flappy Bird";
public int width = 500, height = 500;
public Content c;
public boolean running = false;
public boolean playing = false;
public Thread t;
public Player p;
public Hazards e;
public TitleScreen ts;
public JPanel mainPanel;
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
Engine e = new Engine();
e.execute();
}
});
}
public void execute() {
ts = new TitleScreen(width, height);
e = new Hazards(width, height, 30);
p = new Player(this);
c = new Content(this);
c.setPreferredSize(new Dimension(width, height));
c.setLayout(null);
c.addKeyListener(p);
mainPanel = new JPanel();
mainPanel.setPreferredSize(new Dimension(width, height));
mainPanel.setLayout(null);
f = new JFrame();
f.setTitle(title);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setResizable(false);
f.add(c);
// f.add(mainPanel);
f.pack();
f.createBufferStrategy(2);
f.setLayout(null);
f.setLocationRelativeTo(null);
f.setVisible(true);
c.requestFocus();
//ts.setScreen(mainPanel);
start();
}
public synchronized void start() {
if (running)
return;
running = true;
t = new Thread(this);
t.start();
}
public synchronized void stop() {
if (!running)
return;
running = false;
try {
t.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public void run() {
long lastime = System.nanoTime();
double AmountOfTicks = 60;
double ns = 1000000000 / AmountOfTicks;
double delta = 0;
int tick = 0;
while (running) {
long now = System.nanoTime();
delta += (now - lastime) / ns;
lastime = now;
if (delta >= 1) {
// Call all updates here
if (playing) {
p.updatePos();
tick++;
if (tick == 60) {
tick = 0;
p.distance += p.speed;
System.out.println(p.distance);
if ((p.distance % 4) == 0) {
System.out.println("Making new pipes-----------------------------------------------------");
e.verts.add(new Vertical(600, 10, 30, height - 30, 100));
}
}
for (int x = 0; x < e.verts.size(); x++) {
e.verts.get(x).top.x -= p.speed;
e.verts.get(x).bottom.x -= p.speed;
if(e.verts.get(x).top.x<-50) {
e.verts.remove(x);
System.out.println("removed a pipe");
}
if(p.xPos>e.verts.get(x).top.x && !e.verts.get(x).scoredOn) {
e.verts.get(x).scoredOn = true;
p.score++;
}
}
}
mainPanel.revalidate();
mainPanel.repaint();
f.revalidate();
f.repaint();
delta--;
}
}
}
}
Player class
package main;
import java.awt.Rectangle;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
public class Player implements KeyListener {
public int size = 10;
public double xPos = 50;
public double yPos = 240;
public double gravity = 3.4;
public double jumpForce = 16.6;
public double weight = 1;
public int speed = 2;
public int score = 0;
public int distance = 0;
public boolean jumping = false;
public double jumpTime = 10;
public int timed = 0;
public Rectangle bounds, temp, top, bottom;
public Engine en;
public Player(Engine engine) {
en = engine;
bounds = new Rectangle((int)xPos, (int)yPos, size, size);
}
public void keyTyped(KeyEvent e) {
}
public void keyPressed(KeyEvent e) {
if (e.getKeyCode() == KeyEvent.VK_W && en.playing) {
jumping = true;
} else if (e.getKeyCode() == KeyEvent.VK_SPACE) {
en.playing = !en.playing;
}
if(jumping) {
timed = 0;
jumpForce = 16.6;
}
}
public void keyReleased(KeyEvent e) {
}
public void updatePos() {
// collide with floor or ceiling
for(int x = 0; x < en.e.hors.size(); x++) {
temp = en.e.hors.get(x).bounds;
if(bounds.intersects(temp)) {
en.playing = false;
jumping = false;
timed = 0;
jumpForce = 0;
yPos = 240;
score = 0;
en.e.verts.clear();
distance = 0;
gravity = 3.8;
}
}
// collide with pipe
for(int x =0; x <en.e.verts.size();x++) {
top = en.e.verts.get(x).top;
bottom = en.e.verts.get(x).bottom;
if(bounds.intersects(top)||bounds.intersects(bottom)) {
en.playing = false;
jumping = false;
timed = 0;
jumpForce = 0;
yPos = 240;
score = 0;
gravity =3.4;
en.e.verts.clear();
distance = 0;
}
}
if (jumping && en.playing) {
gravity = 3.4;
yPos -= jumpForce;
jumpForce -= weight;
if (jumpForce == 0) {
jumping = false;
jumpForce = 16.6;
}
}
//if(!jumping && en.playing) {
gravity += 0.1;
//}
System.out.println(gravity);
yPos += gravity;
bounds.setBounds((int)xPos, (int)yPos, size, size);
}
}

Java Game - unknown error

I have an error it everytime I try to start it, it comes up with a blank window and these error messages.
Exception in thread "Thread-2" java.lang.IllegalArgumentException: Color parameter outside of expected range: Red Green
at java.awt.Color.testColorValueRange(Unknown Source)
at java.awt.Color.<init>(Unknown Source)
at java.awt.Color.<init>(Unknown Source)
at java.awt.Color.<init>(Unknown Source)
at com.tutorial.main.HUD.render(HUD.java:32)
at com.tutorial.main.Game.render(Game.java:118)
at com.tutorial.main.Game.run(Game.java:85)
at java.lang.Thread.run(Unknown Source)
I have a suspicion it is something to do with rendering but not sure can someone help.
I have inserted the following codes:
Game
Window
SmartEnemy
HUD
ID
Handler
package com.tutorial.main;
import java.awt.Canvas;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.image.BufferStrategy;
import java.util.Random;
public class Game extends Canvas implements Runnable {
private static final long serialVersionUID = 7580815534084638412L;
public static final int WIDTH = 640, HEIGHT = WIDTH / 12 * 9;
private Thread thread;
private boolean running = true;
private Random r;
private Handler handler;
private HUD hud;
private Spawn spawner;
public Game() {
new Window(WIDTH, HEIGHT, "Lets Build a Game!", this);
handler = new Handler();
hud = new HUD();
spawner = new Spawn(handler, hud);
this.addKeyListener(new KeyInput(handler));
r = new Random();
// for(int i = 0; i <1; i++){
//implementing Player1
handler.addObject(new Player(WIDTH / 2 - 32, HEIGHT / 2 - 32, ID.Player, handler));
handler.addObject(new BasicEnemy(r.nextInt(Game.WIDTH), r.nextInt(Game.HEIGHT), ID.BasicEnemy, handler));
//implementing Player2
//handler.addObject(new Player(WIDTH/2-32, HEIGHT/2+64, ID.Player2));
/*for (int i = 0; i < 1; i++){
//implementing BasicEnemy
handler.addObject(new BasicEnemy(r.nextInt(WIDTH), r.nextInt(HEIGHT), ID.BasicEnemy, handler));
}*/
}
public synchronized void start() {
thread = new Thread(this);
thread.start();
}
public synchronized void stop() {
try {
thread.join();
running = false;
} catch (Exception e) {
e.printStackTrace();
}
}
public void run() {
this.requestFocus();
long lastTime = System.nanoTime();
double amountOfTicks = 60.0;
double ns = 1000000000 / amountOfTicks;
double delta = 0;
long timer = System.currentTimeMillis();
int frames = 0;
while (running) {
long now = System.nanoTime();
delta += (now - lastTime) / ns;
lastTime = now;
while (delta >= 1) {
tick();
delta--;
}
if (running) {
render();
frames++;
if (System.currentTimeMillis() - timer > 1000) {
timer += 1000;
//System.out.println("FPS: " + frames);
frames = 0;
}
}
}
}
private void tick() {
handler.tick();
hud.tick();
spawner.tick();
}
private void render() {
BufferStrategy bs = this.getBufferStrategy();
if (bs == null) {
this.createBufferStrategy(3);
return;
}
Graphics g = bs.getDrawGraphics();
g.setColor(Color.BLACK);
g.fillRect(0, 0, WIDTH, HEIGHT);
handler.render(g);
hud.render(g);
g.dispose();
bs.show();
}
public static float clamp(float
var, float min, float max) {
if (var >= max) {
return var = max;
} else if (var <= min) {
return var = min;
} else {
return var;
}
}
public static void main(String args[]) {
Game game = new Game();
game.start();
}
}
package com.tutorial.main;
import java.awt.Canvas;
import javax.swing.*;
import java.awt.Dimension;
public class Window extends Canvas {
private static final long serialVersionUID = -240840600533728354L;
public Window(int width, int height, String title, Game game) {
JFrame frame = new JFrame(title);
frame.setPreferredSize(new Dimension(width, height));
frame.setMinimumSize(new Dimension(width, height));
frame.setMaximumSize(new Dimension(width, height));
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setResizable(false);
frame.setLocationRelativeTo(null);
frame.add(game);
frame.setVisible(true);
}
}
package com.tutorial.main;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Rectangle;
public class SmartEnemy extends GameObject{
private Handler handler;
private GameObject player;
public SmartEnemy(int x, int y, ID id, Handler handler) {
super(x, y, id);
this.handler = handler;
for(int i = 0; i < handler.object.size(); i++){
if(handler.object.get(i).getId() == ID.Player) player = handler.object.get(i);
}
}
public Rectangle getBounds(){
return new Rectangle((int)x, (int)y, 32, 32);
}
public void tick() {
handler.addObject(new Trail(x, y,ID.Trail, Color.GREEN, 16, 16, 0.02f, handler));
x += velX;
y += velY;
float diffX = x - player.getX() - 8;
float diffY = y - player.getY() - 8;
float distance = (float) Math.sqrt((x - player.getX()) * (x - player.getX()) + (y - player.getY()) * (y - player.getY()));
velX = (float) ((-1.0/distance) * diffX);
velY = (float) ((-1.0/distance) * diffY);
if (y <= 0 || y >= Game.HEIGHT - 37) velY *= -1;
if (x <= 0 || x >= Game.WIDTH - 16) velX*= -1;
}
public void render(Graphics g) {
g.setColor(Color.GREEN);
g.fillRect((int)x, (int)y, 16, 16);
}
}
package com.tutorial.main;
import java.awt.Graphics;
import java.util.LinkedList;
public class Handler {
LinkedList < GameObject > object = new LinkedList < GameObject > ();
public void tick() {
for (int i = 0; i < object.size(); i++) {
GameObject tempObject = object.get(i);
tempObject.tick();
}
};
public void render(Graphics g) {
for (int i = 0; i < object.size(); i++) {
GameObject tempObject = object.get(i);
tempObject.render(g);
}
}
public void addObject(GameObject object) {
this.object.add(object);
}
public void removeObject(GameObject object) {
this.object.remove(object);
}
}
package com.tutorial.main;
import java.awt.Color;
import java.awt.Graphics;
public class HUD {
public static float HEALTH = 100;
private float greenValue = 255;
private int level = 1;
private float score = 0;
public void tick(){
HEALTH = Game.clamp(HEALTH, 0, 100);
greenValue = Game.clamp(greenValue, 0, 255);
greenValue = HEALTH*2;
score++;
}
public void render(Graphics g){
//Background for Health bar
g.setColor(Color.gray);
g.fillRect(15, 15, 200, 32);
//Health Bar
g.setColor(new Color(75, (float) greenValue, 0));
g.fillRect(15, 15, (int) (HEALTH * 2), 32);
g.setColor(Color.WHITE);
g.drawRect(15, 15, 200, 32);
g.drawString("Score: " + score, 15, 60);
g.drawString("Level: " + level, 15, 75);
}
/*int level = 1, point = 0;
//point scoring system
for(int i = 2; i > 1; i++){
if(HEALTH > 0){
point++;
System.out.println(point);
}
}
}*/
private void score(float score){
this.score = score;
}
public float getScore(){
return score;
}
public int getLevel(){
return level;
}
public void setLevel(int level){
this.level = level;
}
}
package com.tutorial.main;
import java.awt.Graphics;
import java.awt.Rectangle;
public abstract class GameObject {
protected float x, y;
protected ID id;
protected float velX, velY;
public GameObject(float x, float y, ID id){
this.x = x;
this.y = y;
this.id = id;
}
public abstract void tick();
public abstract void render(Graphics g);
public abstract Rectangle getBounds();
public void setX(int x){
this.x = x;
}
public void setY(int y){
this.y = y;
}
public int getX(){
return (int) x;
}
public int getY(){
return (int) y;
}
public void setId(ID id){
this.id = id;
}
public ID getId(){
return id;
}
public void setVelX(int velX){
this.velX = velX;
}
public void setVelY(int velY){
this.velY = velY;
}
public float getVelX(){
return velX;
}
public float getVelY(){
return velY;
}
}

The excetion is caused by this constructor call:
new Color(75, (float) greenValue, 0)
You use the Color(float, float, float), since the second parameter has type float. As documented in the javadocs, this constructor takes 3 floats that represent rgb components. Ranges are from 0.0f to 1.0f, not from 0 to 255, which is why you get the error (75 is too large).
It seems like you should not cast the second parameter to make that statement use the Color(int, int, int) constructor.

JAVA program Bouncing Ball, change the size (pulsating) with a boolean. How to do that?

i have looked all over the internet and in my school books but I can't seem to slove my problem.
In my program "bouncing ball" (got the code from our teacher) i need to change the size of the ball from small to bigger and reverse. I understand that i need a boolean to do that and maybe alsow an if statment. This is what I have in the Ball class rigth now regarding the size change:
private boolean changeSize = true;
int maxSize = 10;
int minSize = 1;
public void changeSize(boolean size ){
if(size == maxSize ){
return minSize;
}
else return maxSize;
}
public void changeBallSize(int d, int f){
diameter = d*f;
This is the whole code for the class Ball:
class Ball {
static int defaultDiameter = 10;
static Color defaultColor = Color.yellow;
static Rectangle defaultBox = new Rectangle(0,0,100,100);
// Position
private int x, y;
// Speen and angel
private int dx, dy;
// Size
private int diameter;
// Color
private Color color;
// Bouncing area
private Rectangle box;
// New Ball
public Ball( int x0, int y0, int dx0, int dy0 ) {
x = x0;
y = y0;
dx = dx0;
dy = dy0;
color = defaultColor;
diameter = defaultDiameter;
}
// New color
public void setColor( Color c ) {
color = c;
}
public void setBoundingBox( Rectangle r ) {
box = r;
}
// ball
public void paint( Graphics g ) {
// Byt till bollens färg
g.setColor( color );
g.fillOval( x, y, diameter, diameter );
}
void constrain() {
// Ge absoluta koordinater för det rektangulära området
int x0 = box.x;
int y0 = box.y;
int x1 = x0 + box.width - diameter;
int y1 = y0 + box.height - diameter;
// Setting speed and angels
if (x < x0)
dx = Math.abs(dx);
if (x > x1)
dx = -Math.abs(dx);
if (y < y0)
dy = Math.abs(dy);
if (y > y1)
dy = -Math.abs(dy);
}
// movingt the ball
x = x + dx;
y = y + dy;
constrain();
}
}
I am a total rookie of java! Thanks for the help!

Add the following into your Ball class:
private int changeFlag=-1;
In your constrain() function, just before the last line, after moving the ball:
if(diameter==maxSize) {
changeFlag=-1;
}
else if (diameter==minSize) {
changeFlag=1;
}
diameter=diameter+changeFlag;

Add this code to your Ball Class
private minSize = 1;
private maxSize = 10;
public void setDiameter(int newDiameter) {
this.diameter = newDiameter;
}
public int getMinSize() {
return minSize;
}
public int getMinSize() {
return maxSize;
}
Use this when you use the ball
Ball ball = new Ball(1,1,1,1);
int newDiameter = 10;
if(newDiameter == ball.getMinSize()) {
ball.setDiameter(ball.getMaxSize());
}
id(newDiameter == ball.getMaxSize()) {
ball.setDiameter (ball.getMinSize());
}

I've edited it, is this what you mean?
Main Class:
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JFrame;
public class Main extends JFrame {
public static void main(String[] args) {
new Main();
}
public Main() {
// configure JFrame
setSize(640, 360);
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// create ball
Ball ball = new Ball(this.getWidth()/2, this.getHeight()/2, 50, 100);
add(ball);
Thread t = new Thread(ball);
t.start();
}
public void paint(Graphics g) {
super.paint(g);
Graphics2D g2 = (Graphics2D) g;
}
}
Ball Class:
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import javax.swing.JComponent;
public class Ball extends JComponent implements Runnable {
private int x, y, minDiameter, maxDiameter, currentDiameter, growRate = -1;
private Color color = Color.BLUE;
public Ball(int x, int y, int minDiameter, int maxDiameter) {
this.x = x;
this.y = y;
this.minDiameter = minDiameter;
this.maxDiameter = maxDiameter;
this.currentDiameter = minDiameter;
setVisible(true);
}
#Override
public void run() {
while (true) {
// coerce max and min size
if (this.currentDiameter + growRate > maxDiameter) {
this.currentDiameter = maxDiameter;
this.growRate = -1;
}
if (this.currentDiameter + growRate < minDiameter) {
this.currentDiameter = minDiameter;
this.growRate = 1;
}
this.currentDiameter += this.growRate;
repaint();
try {
Thread.sleep(10);
}
catch(Exception e) {
System.out.println(e.toString());
}
}
}
public void paint(Graphics g) {
super.paint(g);
Graphics2D g2 = (Graphics2D) g;
g2.setRenderingHints(new RenderingHints(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON));
g2.setColor(this.color);
g2.fillOval(this.x, this.y, this.currentDiameter, this.currentDiameter);
}
}

Java NullPointerException in call to paint()

My program is throwing a NullPointerException error upon trying to call the paint method of a ship.
import java.awt.*;
import java.awt.event.*;
public class Ship extends Polygon implements ActionListener, KeyListener {
final static Point[] shape = new Point[4];
final static Point START_POSITION = new Point(400, 300);
private int windowX;
private int windowY;
Point pull;
public Ship(int maxX, int maxY) {
super(shape, START_POSITION, 0);
windowX = maxX;
windowY = maxY;
shipInit();
init(shape);
Point[] pointArray = getPoints();
pull = new Point(0, 0);
}
public void shipInit() {
shape[0] = new Point(0, 0);
shape[1] = new Point(30, 10);
shape[2] = new Point(0, 20);
shape[3] = new Point(10, 10);
}
public void paint(Graphics brush) {
brush.setColor(Color.white);
Point[] points = getPoints();
if (position.x > windowX) {
position.x -= windowX;
} else if (position.x < 0) {
position.x += windowX;
} else if (position.y > windowY) {
position.y -= windowY;
} else if (position.y < 0) {
position.x += windowY;
}
for (int i = 0; i < points.length; i++) {
int x1;
int y1;
int x2;
int y2;
if (i == points.length - 1) {
x1 = (int) points[i].x;
y1 = (int) points[i].y;
x2 = (int) points[0].x;
y2 = (int) points[0].y;
} else {
x1 = (int) points[i].x;
y1 = (int) points[i].y;
x2 = (int) points[i + 1].x;
y2 = (int) points[i + 1].y;
}
brush.drawLine(x1, y1, x2, y2);
}
}
public void move() {
position.x += 2;
position.y += 5;
// position.y += 1;
}
public void accelerate(double acceleration) {
pull.x += (acceleration * Math.cos(Math.toRadians(rotation)));
pull.y += (acceleration * Math.sin(Math.toRadians(rotation)));
}
public void keyPressed(KeyEvent e) {
int keyPressed = e.getKeyCode();
if (keyPressed == KeyEvent.VK_W)
System.out.println("Hi");
if (keyPressed == KeyEvent.VK_UP) {
accelerate(5);
position.x += pull.x;
position.y += pull.y;
}
if (keyPressed == KeyEvent.VK_RIGHT) {
rotation += 5;
}
if (keyPressed == KeyEvent.VK_LEFT) {
rotation -= 5;
}
}
public void keyReleased(KeyEvent e) {
}
public void keyTyped(KeyEvent e) {
}
#Override
public void actionPerformed(ActionEvent arg0) {
// TODO Auto-generated method stub
}
}
And the class the calls the paint
import java.awt.*;
import java.awt.event.*;
class Asteroids extends Game {
private static int frameWidth = 800;
private static int frameHeight = 600;
Ship player;
public Asteroids() {
super("Asteroids!", frameWidth, frameHeight);
init();
}
public void init() {
player = new Ship(800, 600);
this.addKeyListener(player);
repaint();
}
public void paint(Graphics brush) {
brush.setColor(Color.black);
brush.fillRect(0, 0, width,height);
brush.setColor(Color.white);
String hi = "hi";
brush.drawString(hi, 299, 399);
player.paint(brush);
}
public static void main (String[] args) {
new Asteroids();
}
}
The error says that the error is thrown when calling player.paint(brush). Can anyone figure out why?

I have never coded in this before, but a quick trip to the universe of google explained to me that paint() and init() runs on 2 different threads.
That said, your paint() method gets called BEFORE the init() method.
A quick way to fix this would be to have a boolean that gets set inside init()
Like this:
import java.awt.*;
import java.awt.event.*;
class Asteroids extends Game {
private static int frameWidth = 800;
private static int frameHeight = 600;
Ship player;
private boolean hasInitialized; // Initialization check
public Asteroids() {
super("Asteroids!", frameWidth, frameHeight);
init();
}
public void init() {
player = new Ship(800, 600);
this.addKeyListener(player);
hasInitialized = true; // We set the boolean to true to indicate that we have initialized.
repaint();
}
public void paint(Graphics brush) {
if (!hasInitialized) return; // Nope, not ready yet, we'll stop here.
brush.setColor(Color.black);
brush.fillRect(0, 0, width,height);
brush.setColor(Color.white);
String hi = "hi";
brush.drawString(hi, 299, 399);
player.paint(brush);
}
public static void main (String[] args) {
new Asteroids();
}
}
I'm not 100% certain this will fix it, considering you already have init() inside the constructor.
But it's worth a try!
Source: Java, applet: How to block the activation of paint() before init() finishes it's work

My mainBall class wont repaint when i press a key

I created a class that draws a ball on a screen and my goal is to move it with the keys, but the ball stays in one spot. the coordinates of the ball change according to the key presses but not the actual ball itself
import java.applet.Applet;
import java.awt.Color;
import java.awt.Component;
import java.awt.Event;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Rectangle;
import java.util.ArrayList;
import java.util.concurrent.TimeUnit;
public class game extends Applet implements Runnable
{
static final int WIDTH = 450;
static final int HEIGHT = 450;
private Image dbImage;
private Graphics dbg;
public static long NEW_DOT_FREQ = TimeUnit.SECONDS.toMillis(3);
public long lastUpdateTime;
public long timeSinceLastNewDot;
public ArrayList<Ball> BALLS;
Color[] color = {Color.red, Color.blue, Color.green, Color.yellow, Color.magenta, Color.black};
int colorIndex;
static final int NUM_OF_BALLS = 4;
int i;
int t;
MainBall mainBall = new MainBall(100, 100, 10, 10, 100, 100, 0, 0);
Thread updateTime = new updateTime();
public void start()
{
lastUpdateTime = System.currentTimeMillis();
Thread th = new Thread(this);
th.start();//start main game
updateTime.start();
}
public void updateGame()
{
//Get the current time
long currentTime = System.currentTimeMillis();
//Calculate how much time has passed since the last update
long elapsedTime = currentTime - lastUpdateTime;
//Store this as the most recent update time
lastUpdateTime = currentTime;
//Create a new dot if enough time has passed
//Update the time since last new dot was drawn
timeSinceLastNewDot += elapsedTime;
if (timeSinceLastNewDot >= NEW_DOT_FREQ)
{
int newX = randomNumber();
int newY = randomNumber();
debugPrint("New dot created at x:" + newX + ", y:" + newY + ".");
BALLS.add(new Ball(newX, newY, 20, 20));
timeSinceLastNewDot = 0;
}
}
private void debugPrint(String value)
{
System.out.println(value);
}
public class updateTime extends Thread implements Runnable
{
public void run()
{
for(t = 0; ; t++)
{
try
{
Thread.sleep(1000);
}
catch(InterruptedException e){}
}
}
}
public int randomNumber()
{
return (int)(Math.random() * 400);
}
public int getRandomColor()
{
return (int)(Math.random() * 6);
}
public class MainBall
{
int x;
int y;
int width;
int height;
int xpos = 100;
int ypos = 100;
int xspeed = 0;
int yspeed = 0;
public MainBall(int x, int y, int width, int height, int xpos, int ypos, int xspeed, int yspeed)
{
this.x = 100;
this.y = 100;
this.width = 10;
this.height = 10;
this.xpos = 100;
this.ypos = 100;
this.xspeed = 0;
this.yspeed = 0;
}
public void paintMainBall(Graphics g)
{
g.setColor(Color.black);
g.fillOval(x, y, width, height);
g.drawString(xpos + ", " + ypos, 20, 40);
}
}//mainBall
class Ball
{
int x;
int y;
int width;
int height;
public Ball(int x, int y, int width, int height)
{
this.x = x;
this.y = y;
this.width = width;
this.height = height;
}//end ball
public void paint(Graphics g)
{
g.setColor(color[getRandomColor()]);
g.fillOval(x, y, width, height);
}//end paint
}//ball class
public void update(Graphics g)//double buffer don't touch!!
{
if(dbImage == null)
{
dbImage = createImage(this.getSize().width, this.getSize().height);
dbg = dbImage.getGraphics();
}
dbg.setColor(getBackground());
dbg.fillRect(0, 0, this.getSize().width, this.getSize().height);
dbg.setColor(getForeground());
paint(dbg);
g.drawImage(dbImage, 0, 0, this);
}
public boolean keyDown (Event e, int key)
{
if(key == Event.LEFT)
{
mainBall.xspeed = -5;
mainBall.yspeed = 0;
}
if(key == Event.RIGHT)
{
mainBall.xspeed = 5;
mainBall.yspeed = 0;
}
if(key == Event.UP)
{
mainBall.yspeed = -5;
mainBall.xspeed = 0;
}
if(key == Event.DOWN)
{
mainBall.yspeed = 5;
mainBall.xspeed = 0;
}
return true;
}
public void run()
{
while(true)
{
repaint();
if (mainBall.xpos < 1)
{
mainBall.xpos = 449;
}
if (mainBall.xpos > 449)
{
mainBall.xpos = 1;
}
if (mainBall.ypos < 1)
{
mainBall.ypos = 449;
}
if (mainBall.ypos > 449)
{
mainBall.ypos = 1;
}
mainBall.ypos += mainBall.yspeed;
mainBall.xpos += mainBall.xspeed;
try
{
Thread.sleep(20);
}
catch(InterruptedException ex){}
}
}
public void init()
{
this.setSize(WIDTH, HEIGHT);
BALLS = new ArrayList<Ball>();
}
public void paint(Graphics g)
{
g.drawString("time: " + t, 20, 20);
mainBall.paintMainBall(g);
for (Ball ball : BALLS)
{
ball.paint(g);
}
updateGame();
}
}

You update the xPos/yPos values of the ball, but never the x/y values
public void paintMainBall(Graphics g) {
System.out.println("PaintMainBall");
g.setColor(Color.RED);
g.fillOval(x, y, width, height);
g.drawString(xpos + ", " + ypos, 20, 40);
}