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Game Development lock canvas error

i keep getting error draw to canvas
Error
The error keep happening when I tried to draw to the canvas the player after the user move the joystick
it always writes me "cant lock canvas ,canvas already locked"
i'm kind of beginner in game development and sorry if the question is a little unclear if you need more details just say and I will send you more info
Main class - the main activity
package app.shahardagan.Raven;
import android.graphics.Point;
import android.os.Bundle;
import android.app.Activity;
import android.view.Display;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.ImageView;
import android.widget.RelativeLayout;
public class Main extends Activity {
RelativeLayout layout_joystick;
ImageView image_joystick, image_border;
GameEngine gameEngine;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Get a Display object to access screen details
Display display = getWindowManager().getDefaultDisplay();
// Load the resolution into a Point object
Point size = new Point();
size.set(display.getWidth(),display.getHeight());
layout_joystick = (RelativeLayout)findViewById(R.id.layout_joystick);
gameEngine = new GameEngine(this,size.x,size.y);
setContentView(gameEngine);
}
#Override
protected void onResume(){
super.onResume();
gameEngine.resume();
}
#Override
protected void onPause(){
super.onPause();
gameEngine.pause();
}
}
GameEngine class - responsible to draw the player and update the game
package app.shahardagan.Raven;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.drawable.Drawable;
import android.util.Log;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.widget.ImageView;
import android.widget.RelativeLayout;
public class GameEngine extends SurfaceView implements Runnable {
JoyStickClass js;
// This is our thread
private Thread gameThread = null;
// This is new. We need a SurfaceHolder
// When we use Paint and Canvas in a thread
// We will see it in action in the draw method soon.
private SurfaceHolder ourHolder;
// A boolean which we will set and unset
// when the game is running- or not.
private volatile boolean playing;
// Game is paused at the start
private boolean paused = true;
// A Canvas and a Paint object
private Canvas canvas;
private Paint paint;
// How wide and high is the screen?
private int screenX;
private int screenY;
// This variable tracks the game frame rate
private long fps;
// This is used to help calculate the fps
private long timeThisFrame;
private Context context;
private Player player;
private Drawable playerImage;
public GameEngine(Context context, int x, int y) {
// This calls the default constructor to setup the rest of the object
super(context);
this.context = context;
// Initialize ourHolder and paint objects
ourHolder = getHolder();
paint = new Paint();
// Initialize screenX and screenY because x and y are local
screenX = x;
screenY = y;
prepareLevel();
}
private void prepareLevel(){
player = new Player(context,screenX,screenY);
}
public void PlayerControls(Context context,RelativeLayout layout_joystick, ImageView image_joystick, ImageView image_border){
js = new JoyStickClass(context, layout_joystick, R.drawable.image_button);
js.setStickSize(150, 150);
js.setLayoutSize(500, 500);
js.setLayoutAlpha(150);
js.setStickAlpha(100);
js.setOffset(90);
js.setMinimumDistance(50);
layout_joystick.setOnTouchListener(new View.OnTouchListener() {
public boolean onTouch(View arg0, MotionEvent arg1) {
js.drawStick(arg1);
if(arg1.getAction() == MotionEvent.ACTION_DOWN || arg1.getAction() == MotionEvent.ACTION_MOVE) {
int direction = js.get8Direction();
if(direction == JoyStickClass.STICK_UP) {
} else if(direction == JoyStickClass.STICK_UPRIGHT) {
player.setMovementState(Player.UP);
} else if(direction == JoyStickClass.STICK_RIGHT) {
} else if(direction == JoyStickClass.STICK_DOWNRIGHT) {
} else if(direction == JoyStickClass.STICK_DOWN) {
} else if(direction == JoyStickClass.STICK_DOWNLEFT) {
} else if(direction == JoyStickClass.STICK_LEFT) {
} else if(direction == JoyStickClass.STICK_UPLEFT) {
} else if(direction == JoyStickClass.STICK_NONE) {
}
} else if(arg1.getAction() == MotionEvent.ACTION_UP) {
}
return true;
}
});
}
// Runs when the OS calls onPause on BreakoutActivity method
public void pause() {
playing = false;
try {
gameThread.join();
} catch (InterruptedException e) {
Log.e("Error:", "joining thread");
}
}
// Runs when the OS calls onResume on BreakoutActivity method
public void resume() {
playing = true;
gameThread = new Thread(this);
gameThread.start();
}
#Override
public void run() {
while (playing) {
// Capture the current time in milliseconds in startFrameTime
long startFrameTime = System.currentTimeMillis();
// Update the frame
// Update the frame
if(!paused){
update();
}
// Draw the frame
draw();
// Calculate the fps this frame
// We can then use the result to
// time animations and more.
timeThisFrame = System.currentTimeMillis() - startFrameTime;
if (timeThisFrame >= 1) {
fps = 1000 / timeThisFrame;
}
}
}
private void draw() {
// Make sure our drawing surface is valid or game will crash
if (ourHolder.getSurface().isValid()) {
// Lock the canvas ready to draw
canvas = ourHolder.lockCanvas();
// Draw the background color
canvas.drawColor(Color.argb(255, 26, 128, 182));
// Draw everything to the screen
// Choose the brush color for drawing
paint.setColor(Color.argb(255, 255, 255, 255));
canvas.drawBitmap(player.getBitmap(),player.getX(),screenY - player.getHeight(),paint);
}
}
private void update() {
player.update(fps);
}
}
Player class - the player class methods
package app.shahardagan.Raven;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.RectF;
public class Player {
// RectF is an object that holds four coordinates - just what we need
private RectF rect;
private Bitmap bitmap;
// How long will our paddle will be
private float length;
private float height;
// X is the far left of the rectangle which forms our paddle
private float x;
private float y;
// Which ways can the player move
final int STOPPED = 0;
public static final int UP = 1;
public static final int UPRIGHT = 2;
public static final int RIGHT = 3;
public static final int DOWNRIGHT = 4;
public static final int DOWN = 5;
public static final int DOWNLEFT = 6;
public static final int LEFT = 7;
public static final int UPLEFT = 8;
// Is the paddle moving and in which direction
private int playerMoving = STOPPED;
private int playerSpeed;
public Player(Context context,int screenX, int screenY){
rect = new RectF();
length =screenX/10;
height = screenX/10;
x = screenX;
y= 0;
bitmap = BitmapFactory.decodeResource(context.getResources(),R.drawable.eagle_fly);
bitmap = Bitmap.createScaledBitmap(bitmap,(int)length,(int)height,false);
playerSpeed = 350;
}
public RectF getRect(){
return rect;
}
public Bitmap getBitmap(){
return bitmap;
}
public float getX(){ return x; }
public float getHeight(){return height;}
private float getLength(){return length;}
public void setMovementState(int state){
playerMoving = state;
}
void update(long fps){
if(playerMoving == LEFT){
x = x - playerSpeed / fps;
}
if(playerMoving == RIGHT){
x = x + playerSpeed / fps;
}
rect.top = y;
rect.bottom = y+ height;
rect.left = x;
rect.right = x + length;
}
}
Joy stick class
package app.shahardagan.Raven;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewGroup.LayoutParams;
public class JoyStickClass {
public static final int STICK_NONE = 0;
public static final int STICK_UP = 1;
public static final int STICK_UPRIGHT = 2;
public static final int STICK_RIGHT = 3;
public static final int STICK_DOWNRIGHT = 4;
public static final int STICK_DOWN = 5;
public static final int STICK_DOWNLEFT = 6;
public static final int STICK_LEFT = 7;
public static final int STICK_UPLEFT = 8;
private int STICK_ALPHA = 200;
private int LAYOUT_ALPHA = 200;
private int OFFSET = 0;
private Context mContext;
private ViewGroup mLayout;
private LayoutParams params;
private int stick_width, stick_height;
private int position_x = 0, position_y = 0, min_distance = 0;
private float distance = 0, angle = 0;
private DrawCanvas draw;
private Paint paint;
private Bitmap stick;
private boolean touch_state = false;
public JoyStickClass (Context context, ViewGroup layout, int stick_res_id) {
mContext = context;
stick = BitmapFactory.decodeResource(mContext.getResources(),
stick_res_id);
stick_width = stick.getWidth();
stick_height = stick.getHeight();
draw = new DrawCanvas(mContext);
paint = new Paint();
mLayout = layout;
params = mLayout.getLayoutParams();
}
public void drawStick(MotionEvent arg1) {
position_x = (int) (arg1.getX() - (params.width / 2));
position_y = (int) (arg1.getY() - (params.height / 2));
distance = (float) Math.sqrt(Math.pow(position_x, 2) + Math.pow(position_y, 2));
angle = (float) cal_angle(position_x, position_y);
if(arg1.getAction() == MotionEvent.ACTION_DOWN) {
if(distance <= (params.width / 2) - OFFSET) {
draw.position(arg1.getX(), arg1.getY());
draw();
touch_state = true;
}
} else if(arg1.getAction() == MotionEvent.ACTION_MOVE && touch_state) {
if(distance <= (params.width / 2) - OFFSET) {
draw.position(arg1.getX(), arg1.getY());
draw();
} else if(distance > (params.width / 2) - OFFSET){
float x = (float) (Math.cos(Math.toRadians(cal_angle(position_x, position_y))) * ((params.width / 2) - OFFSET));
float y = (float) (Math.sin(Math.toRadians(cal_angle(position_x, position_y))) * ((params.height / 2) - OFFSET));
x += (params.width / 2);
y += (params.height / 2);
draw.position(x, y);
draw();
} else {
mLayout.removeView(draw);
}
} else if(arg1.getAction() == MotionEvent.ACTION_UP) {
mLayout.removeView(draw);
touch_state = false;
}
}
public int[] getPosition() {
if(distance > min_distance && touch_state) {
return new int[] { position_x, position_y };
}
return new int[] { 0, 0 };
}
public int getX() {
if(distance > min_distance && touch_state) {
return position_x;
}
return 0;
}
public int getY() {
if(distance > min_distance && touch_state) {
return position_y;
}
return 0;
}
public float getAngle() {
if(distance > min_distance && touch_state) {
return angle;
}
return 0;
}
public float getDistance() {
if(distance > min_distance && touch_state) {
return distance;
}
return 0;
}
public void setMinimumDistance(int minDistance) {
min_distance = minDistance;
}
public int getMinimumDistance() {
return min_distance;
}
public int get8Direction() {
if(distance > min_distance && touch_state) {
if(angle >= 247.5 && angle < 292.5 ) {
return STICK_UP;
} else if(angle >= 292.5 && angle < 337.5 ) {
return STICK_UPRIGHT;
} else if(angle >= 337.5 || angle < 22.5 ) {
return STICK_RIGHT;
} else if(angle >= 22.5 && angle < 67.5 ) {
return STICK_DOWNRIGHT;
} else if(angle >= 67.5 && angle < 112.5 ) {
return STICK_DOWN;
} else if(angle >= 112.5 && angle < 157.5 ) {
return STICK_DOWNLEFT;
} else if(angle >= 157.5 && angle < 202.5 ) {
return STICK_LEFT;
} else if(angle >= 202.5 && angle < 247.5 ) {
return STICK_UPLEFT;
}
} else if(distance <= min_distance && touch_state) {
return STICK_NONE;
}
return 0;
}
public int get4Direction() {
if(distance > min_distance && touch_state) {
if(angle >= 225 && angle < 315 ) {
return STICK_UP;
} else if(angle >= 315 || angle < 45 ) {
return STICK_RIGHT;
} else if(angle >= 45 && angle < 135 ) {
return STICK_DOWN;
} else if(angle >= 135 && angle < 225 ) {
return STICK_LEFT;
}
} else if(distance <= min_distance && touch_state) {
return STICK_NONE;
}
return 0;
}
public void setOffset(int offset) {
OFFSET = offset;
}
public int getOffset() {
return OFFSET;
}
public void setStickAlpha(int alpha) {
STICK_ALPHA = alpha;
paint.setAlpha(alpha);
}
public int getStickAlpha() {
return STICK_ALPHA;
}
public void setLayoutAlpha(int alpha) {
LAYOUT_ALPHA = alpha;
mLayout.getBackground().setAlpha(alpha);
}
public int getLayoutAlpha() {
return LAYOUT_ALPHA;
}
public void setStickSize(int width, int height) {
stick = Bitmap.createScaledBitmap(stick, width, height, false);
stick_width = stick.getWidth();
stick_height = stick.getHeight();
}
public void setStickWidth(int width) {
stick = Bitmap.createScaledBitmap(stick, width, stick_height, false);
stick_width = stick.getWidth();
}
public void setStickHeight(int height) {
stick = Bitmap.createScaledBitmap(stick, stick_width, height, false);
stick_height = stick.getHeight();
}
public int getStickWidth() {
return stick_width;
}
public int getStickHeight() {
return stick_height;
}
public void setLayoutSize(int width, int height) {
params.width = width;
params.height = height;
}
public int getLayoutWidth() {
return params.width;
}
public int getLayoutHeight() {
return params.height;
}
private double cal_angle(float x, float y) {
if(x >= 0 && y >= 0)
return Math.toDegrees(Math.atan(y / x));
else if(x < 0 && y >= 0)
return Math.toDegrees(Math.atan(y / x)) + 180;
else if(x < 0 && y < 0)
return Math.toDegrees(Math.atan(y / x)) + 180;
else if(x >= 0 && y < 0)
return Math.toDegrees(Math.atan(y / x)) + 360;
return 0;
}
private void draw() {
try {
mLayout.removeView(draw);
} catch (Exception e) { }
mLayout.addView(draw);
}
private class DrawCanvas extends View{
float x, y;
private DrawCanvas(Context mContext) {
super(mContext);
}
public void onDraw(Canvas canvas) {
canvas.drawBitmap(stick, x, y, paint);
}
private void position(float pos_x, float pos_y) {
x = pos_x - (stick_width / 2);
y = pos_y - (stick_height / 2);
}
}
}

In your draw() method, you're locking the Canvas, but not unlocking the Canvas after you finish drawing. So, when you re-enter your draw method, the Canvas is still locked from the previous call.
You likely need to add unlockCanvasAndPost(Canvas canvas) after you finish drawing. See the full docs here.

How would I test collision for 2 images in Java.

I am currently making a Space Shooter in Java. I am able to make bullets shoot and enemies come from the top, but I am not sure how to check if they intersect. I understand that the Rectangle class has a intersects method, but I am not sure how I would place the rectangles around the bullets and the enemies, since I don't know beforehand how many may be on the screen. How can I do this? Here is my code:
Game.java
package main;
import java.awt.Canvas;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.image.BufferStrategy;
import java.awt.image.BufferedImage;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
public class Game extends Canvas implements Runnable, KeyListener {
//declare values
private static final long serialVersionUID = 1L;
public static final int WIDTH = 800;
public static final int HEIGHT = 600;
public static final String TITLE = "Space Shooter";
private boolean running = false;
private Thread thread;
private Player player;
private BufferedImage playerImage;
private BufferedImage bulletImage;
private BufferedImage enemyImage;
int playerx;
int playery;
int round = 1;
public Game() {
//
player = new Player((WIDTH/2)-32, HEIGHT-200);
//allocates all file resources
try {
playerImage = ImageIO.read(this.getClass().getResourceAsStream("/resources/player.png"));
bulletImage = ImageIO.read(this.getClass().getResourceAsStream("/resources/bullet.png"));
enemyImage = ImageIO.read(this.getClass().getResourceAsStream("/resources/enemy.png"));
} catch (IOException e) {
e.printStackTrace();
}
addKeyListener(this);
setFocusable(true);
requestFocusInWindow();
}
//starts thread
private synchronized void start() {
if (running)
return;
running = true;
thread = new Thread(this);
thread.start();
}
//stops thread
private synchronized void stop() {
if (!running)
return;
running = false;
try {
thread.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.exit(1);
}
#Override
//game loop
public void run() {
long lastTime = System.nanoTime();
final double amountOfTicks = 60.0;
double ns = 1000000000 / amountOfTicks;
double delta = 0;
int updates = 0;
int frames = 0;
long timer = System.currentTimeMillis();
while (running) {
long now = System.nanoTime();
delta += (now - lastTime) / ns;
lastTime = now;
if (delta > 1) {
tick();
updates++;
delta--;
}
Shoot.updateBullets();
Enemy.updateEnemies();
render();
frames++;
if (System.currentTimeMillis() - timer > 1000) {
timer += 1000;
System.out.println(updates + " TICKS, " + frames + " FPS");
updates = 0;
frames = 0;
}
}
stop();
}
//updates sprite locations
public void tick() {
playerx = player.getX();
playery = player.getY();
}
//renders sprites
public void render() {
//setting up triple-buffering
BufferStrategy bs = this.getBufferStrategy();
if (bs == null) {
createBufferStrategy(3);
return;
}
Graphics g = bs.getDrawGraphics();
//////////////////////////////////
g.setColor(Color.BLACK); g.fillRect(0,0,getWidth(), getHeight());
g.drawImage(playerImage, playerx, playery, this);
if (Shoot.allBullets.size() != 0) {
for (int i = 0; i < Shoot.allBullets.size(); i++) {
int bulletx = (int) Shoot.allBullets.get(i).x;
int bullety = (int) Shoot.allBullets.get(i).y;
g.drawImage(bulletImage, bulletx + 21, bullety, this);
}
}
if (Enemy.allEnemies.size() != 0) {
for (int i = 0; i < Enemy.allEnemies.size(); i++) {
int enemyx = (int) Enemy.allEnemies.get(i).x;
int enemyy = (int) Enemy.allEnemies.get(i).y;
g.drawImage(enemyImage, enemyx, enemyy, this);
}
} else {
Enemy.createEnemies(round);
round++;
}
//////////////////////////////////
g.dispose();
bs.show();
}
#Override
public void keyReleased(KeyEvent e) {
int key = e.getKeyCode();
if (key == KeyEvent.VK_SPACE) {
Shoot.addBullet(player.getX(), player.getY());
}
}
public void keyPressed(KeyEvent e) {
int key = e.getKeyCode();
if (key == KeyEvent.VK_UP) {
player.setY(playery -= 20);
} else if (key == KeyEvent.VK_DOWN) {
player.setY(playery += 20);
} else if (key == KeyEvent.VK_RIGHT) {
player.setX(playerx += 40);
} else if (key == KeyEvent.VK_LEFT) {
player.setX(playerx -= 40);
}
}
public void keyTyped(KeyEvent e) {}
public static void main(String[] args) {
Game game = new Game();
JFrame frame = new JFrame(TITLE);
frame.setSize(WIDTH, HEIGHT);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setResizable(false);
frame.add(game);
frame.getContentPane().setBackground(Color.BLACK);
frame.setVisible(true);
game.start();
}
}
Shoot.java
package main;
import java.util.ArrayList;
public class Shoot {
static ArrayList<Point> allBullets = new ArrayList<Point>();
public static void addBullet(int x, int y) {
allBullets.add(new Point(x, y));
}
public static ArrayList<Point> getAllBulletPosistions() {
return allBullets;
}
public static void updateBullets() {
if (allBullets.size() != 0) {
for (int i = 0; i < allBullets.size(); i++) {
allBullets.get(i).y -= 1;
}
}
}
}
Enemy.java
package main;
import java.util.ArrayList;
public class Enemy {
static ArrayList<Point> allEnemies = new ArrayList<Point>();
public static ArrayList<Point> createEnemies(int round) {
for (int i = 0; i < round; i++) {
Point newEnemyLocation = new Point((int) (Math.random()*Game.WIDTH - 64), 0);
if (newEnemyLocation.x < 64) {
newEnemyLocation.x += 70;
}
allEnemies.add(newEnemyLocation);
}
return allEnemies;
}
int validate(int xpos) {
if (xpos > Game.WIDTH - 64) {
xpos -= 64;
}
if (xpos < 64) {
xpos += 64;
}
return xpos;
}
public static ArrayList<Point> updateEnemies() {
if (allEnemies.size() != 0) {
for (int i = 0; i < allEnemies.size(); i++) {
Point enemyLocation = allEnemies.get(i);
if (enemyLocation.y <= Game.HEIGHT) {
allEnemies.get(i).y += 0.1;
} else {
allEnemies.remove(i);
}
}
}
return allEnemies;
}
}

for(int i = 0; i < Shoot.allBullets.size(); i++){
for(int j = 0; j < Enemy.allEnemys.size(); j++){
if(new Rectangle(Shoot.allBullets.get(i).x,Shoot.allBullets.get(i).y, width, height).intersects(new Rectangle(Enemy.allEnemys.get(j).x, Enemy.allEnemys.get(j).y, width, height)){
//on intersect
}
}
}
This would work but you shouldn't create new rectangles like this instead you should create a bullet class and a Enemy class that both contains the position and Rectangle anyways good luck!

Typing game: choosing two words

I'm creating a game like zType
and I have a problem in validating the input. As you can see in the picture below it select two words. How can I fix this problem, please help.
This is My Game class
import java.awt.Canvas;
import java.awt.event.KeyListener;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.image.BufferStrategy;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.LinkedList;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
public class Game extends Canvas implements Runnable, KeyListener
{
public static final int WIDTH = 640;
public static final int HEIGHT = 680;
public final String TITLE = "Game";
private boolean running = false;
private Thread thread;
private BufferedImage spriteSheet = null;
private BufferedImage background = null;
public int level = 1;
public int fps = 0;
public int score = 0;
private int enemy_count = 15;
private int enemy_killed = 0;
private int enemy_notkilled = 0;
private boolean target = false;
public String t = "";
private Controller c;
private Textures tex;
private LinkedList<Enemy> e = new LinkedList<Enemy>();
private Enemy enemy;
public void init()
{
requestFocus();
try
{
spriteSheet = ImageIO.read(getClass().getResource("/sprite_sheet.png"));
background = ImageIO.read(getClass().getResource("/background.png"));
}
catch(IOException e)
{
e.printStackTrace();
}
tex = new Textures(this);
c = new Controller(tex, this);
addKeyListener(this);
c.createEnemy(enemy_count);
e = c.getEnemy();
}
private synchronized void start()
{
if(running)
return;
running = true;
thread = new Thread(this);
thread.start();
}
private synchronized void stop()
{
if(!running)
return;
running = false;
try
{
thread.join();
}
catch(InterruptedException e)
{
e.printStackTrace();
}
System.exit(1);
}
public void run()
{
init();
long lastTime = System.nanoTime();
final double amountOfTicks= 60.0;
double ns = 1000000000 / amountOfTicks;
double delta = 0;
int frames = 0;
long timer = System.currentTimeMillis();
while(running)
{
long now = System.nanoTime();
delta += (now - lastTime) / ns;
lastTime = now;
if(delta >= 1)
{
update();
delta--;
}
render();
frames++;
if(System.currentTimeMillis() - timer > 1000)
{
timer += 1000;
fps = frames;
frames = 0;
}
}
stop();
}
private void update()
{
c.update();
if(enemy_killed + enemy_notkilled >= enemy_count)
{
e.clear();
t = "";
level++;
enemy_killed = 0;
enemy_notkilled = 0;
c.createEnemy(enemy_count);
}
}
private void render()
{
BufferStrategy bs = this.getBufferStrategy();
if(bs == null)
{
createBufferStrategy(3);
return;
}
Graphics g = bs.getDrawGraphics();
g.drawImage(background, 0, 0, null);
c.render(g);
g.dispose();
bs.show();
}
public void keyPressed(KeyEvent ek)
{
int key = ek.getKeyCode();
char character = Character.toLowerCase(ek.getKeyChar());
boolean result = isValid(key);
if(result && !target)
{
for(int i = 0; i < e.size(); i++)
if(e.get(i).getFirstLetter() == character && e.get(i).getOnScreen())
{
enemy = e.get(i);
t = enemy.getText();
if(enemy.getCurrentIndex() == 0)
enemy.addCurrentIndex();
target = true;
System.out.println("---"+enemy.text);
break;
}
}
else if(result && t.charAt(enemy.getCurrentIndex()) == character)
enemy.addCurrentIndex();
}
public void keyReleased(KeyEvent ek){ }
public void keyTyped(KeyEvent ek){ }
public static void main(String[] args)
{
Game game = new Game();
game.setPreferredSize(new Dimension(WIDTH, HEIGHT));
game.setMaximumSize(new Dimension(WIDTH, HEIGHT));
game.setMinimumSize(new Dimension(WIDTH, HEIGHT));
JFrame frame = new JFrame(game.TITLE);
frame.add(game);
frame.pack();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setResizable(false);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
game.start();
}
public boolean isValid(int key)
{
return key >= 65 && key <= 90 ? true : false;
}
public BufferedImage getSpriteSheet()
{
return spriteSheet;
}
public int getEnemy_count()
{
return enemy_count;
}
public void setEnemy_count(int enemy_count)
{
this.enemy_count = enemy_count;
}
public int getEnemy_killed()
{
return enemy_killed;
}
public void setEnemy_killed(int enemy_killed)
{
this.enemy_killed = enemy_killed;
}
public int getEnemy_notkilled()
{
return enemy_notkilled;
}
public void setEnemy_notkilled(int enemy_notkilled)
{
this.enemy_notkilled = enemy_notkilled;
}
public void addScore(int k)
{
score += k;
}
public void falseTarget()
{
target = false;
}
public String getT()
{
return t;
}
public void setT(String k)
{
t = k;
}
}
This is my Enemy Class
import java.awt.*;
import java.awt.font.TextAttribute;
import java.text.AttributedString;
public class Enemy
{
private double x ,y;
public String text;
private char firstLetter;
private AttributedString as;
private Controller c;
private Textures tex;
private Game game;
private int currentIndex = 0;
private int textLength = 0;
private double speed = 0.0;
private int stringWidth = 0;
private boolean onScreen = false;
public Enemy(double x, double y, double speed, Textures tex, Controller c, Game game, String text, int stringWidth)
{
this.x = x;
this.y = y;
this.tex = tex;
this.text = text;
this.game = game;
this.c = c;
this.speed = speed;
firstLetter = this.text.charAt(0);
textLength = this.text.length();
this.stringWidth = stringWidth;
}
public void update()
{
y += speed;
if(y >= 0)
onScreen = true;
if(currentIndex >= textLength)
{
game.addScore(5);
game.setT("");
c.removeEnemy(this);
game.setEnemy_killed(game.getEnemy_killed() + 1);
game.falseTarget();
}
if(y >= Game.HEIGHT - 50)
{
//game.decreaseHealth();
game.setT("");
c.removeEnemy(this);
game.setEnemy_notkilled(game.getEnemy_notkilled() + 1);
game.falseTarget();
game.t ="";
}
}
public void render(Graphics g)
{
g.drawImage(tex.enemy, (int)x, (int)y, null);
as = new AttributedString(text);
if(currentIndex >= 1)
as.addAttribute(TextAttribute.FOREGROUND, Color.WHITE, 0, currentIndex);
as.addAttribute(TextAttribute.FONT, new Font("Consolas", Font.BOLD, 12), 0, text.length());
g.drawString(as.getIterator(), (int)x + getAdd(stringWidth), (int)y + 13);
}
public double getX()
{
return x;
}
public double getY()
{
return y;
}
public String getText()
{
return text;
}
public char getFirstLetter()
{
return firstLetter;
}
public void addCurrentIndex()
{
currentIndex++;
}
public int getCurrentIndex()
{
return currentIndex;
}
public int getTextLength()
{
return textLength;
}
public int getAdd(int width)
{
return (96 / 2) - (width / 2);
}
public boolean getOnScreen()
{
return onScreen;
}
}

The problem is that you're calling falseTarget() whenever an enemy moves out of the screen. In your example, you assigned target = true when you pressed the 'o' (for the enemy named "owe"), but then a different enemy (maybe "jet", maybe an enemy that is no longer visible) finished "dropping" out of the screen (y >= Game.HEIGHT - 50), so you called falseTarget() - and thus, when you pressed 'i' you started a new enemy ("ice").
What you want to do is call falseTarget() in this case only if the enemy that dropped out of the screen is the one that's currently being targeted:
if(y >= Game.HEIGHT - 50)
{
//game.decreaseHealth();
//game.setT(""); // <-- Commented this line out
c.removeEnemy(this);
game.setEnemy_notkilled(game.getEnemy_notkilled() + 1);
if(game.getT().equals(text)) // <-- Added this if before calling falseTarget()
{ // and clearing the game's current enemy text
game.falseTarget();
game.t ="";
}
}

onDraw(Canvas canvas) never reached?

Can anyone help, my app does not seem to do the onDraw() in the GraView class, even if .invalidate is called upon from either inside or outside the class. I managed to figure out with system.err that it does invalidate the view, however it never gets in the onDraw( ), even though the rest of the app keeps running. I found a lot of solutionssuggesting putting setWillNotDraw(false) in the constructor, but that did not solve anything.
GravIO.java File:
package dabawi.gravitas;
import android.app.Activity;
import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
public class GravIO extends Activity implements Runnable, OnTouchListener {
public final static int clock = 1000;
private GravEngine engine;
private GraView TV;
private SensorManager mSensorManager;
private Sensor mSensor;
private Thread t1;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
t1 = new Thread(this);
t1.start();
engine = new GravEngine();
TV = new GraView(this, engine);
setContentView(TV);
TV.setOnTouchListener(this);
TV.setVisibility(View.VISIBLE);
//mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
System.err.println("Starting Engine") ;
run();
}
#Override
public void run() {
while (true) {
try {
System.err.println("Tik") ;
engine.tick();
TV.invalidate();
Thread.sleep(GravIO.clock);
} catch (InterruptedException ex) {
System.err.println("faal");
}
}
}
#Override
public boolean onTouch(View view, MotionEvent event) {
engine.switchGravity();
return true;
}
}
GraView.java File:
package dabawi.gravitas;
import android.annotation.SuppressLint;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.view.Display;
import android.view.View;
import android.view.WindowManager;
#SuppressLint({ "DrawAllocation", "ViewConstructor" })
public class GraView extends View {
private GravEngine engine;
private int screenWidth, screenHeight, ySpace = 5, xSpace, scale;
private Paint paint;
private int xLoc, yLoc;
private boolean xWall = false, yWall = false;
public GraView(Context context, GravEngine engine) {
super(context);
setWillNotDraw(false);
this.engine = engine;
calcScale(context);
}
#Override // We think the problem is with this method, that it is never called upon.
public void onDraw(Canvas canvas) {
super.onDraw(canvas);
System.err.println("Calculating position");
calcPos();
canvas = new Canvas();
// drawing background
paint = new Paint();
paint.setStyle(Paint.Style.FILL);
paint.setColor(Color.WHITE);
canvas.drawPaint(paint);
drawGame(canvas);
}
private void drawGame(Canvas canvas) {
drawRoom(canvas);
drawPlayer(canvas);
}
#SuppressWarnings("deprecation")
private void calcScale(Context context) {
WindowManager wm = (WindowManager) context
.getSystemService(Context.WINDOW_SERVICE);
Display d = wm.getDefaultDisplay();
screenWidth = d.getWidth();
screenHeight = d.getHeight();
scale = screenHeight / ySpace;
xSpace = screenWidth / scale;
}
private void calcPos() {
xLoc = (engine.getxPlayer() / GravEngine.roomScaling);
yLoc = (engine.getyPlayer() / GravEngine.roomScaling);
if (xLoc < (xSpace + 1) / 2) {
xLoc = (xSpace + 1) / 2;
xWall = true;
} else if (xLoc > (GravRoom.xSize - ((xSpace + 1) / 2))) {
xLoc = GravRoom.xSize - ((xSpace + 1) / 2);
xWall = true;
} else {
xWall = false;
}
if (yLoc < (ySpace + 1) / 2) {
yLoc = (ySpace + 1) / 2;
yWall = true;
} else if (yLoc > (GravRoom.xSize - ((ySpace + 1) / 2))) {
xLoc = GravRoom.ySize - ((ySpace + 1) / 2);
yWall = true;
} else {
yWall = false;
}
}
private void drawPlayer(Canvas canvas) {
float xPos = engine.getxPlayer() / GravEngine.roomScaling, yPos = engine
.getyPlayer() / GravEngine.roomScaling;
if (xWall) {
}
if (yWall) {
}
paint.setColor(Color.BLUE);
int left = (int) (xPos * scale), top = (int) (yPos * scale);
int right = left + (GravEngine.pxSize / GravEngine.roomScaling) * scale;
int bot = top + (GravEngine.pySize / GravEngine.roomScaling) * scale;
canvas.drawRect(left, top, right, bot, paint);
}
private void drawRoom(Canvas canvas) {
for (int i = 0, x = xLoc - ((xSpace + 1) / 2); i < xSpace + 1; x++, i++) {
for (int j = 0, y = yLoc - ((ySpace + 1) / 2); i < ySpace + 1; y++, j++) {
drawRoomPart(x,y,i,j,canvas);
}
}
}
private void drawRoomPart(int x, int y, int i, int j, Canvas canvas) {
if (x >= 0 && y >= 0 && x < GravRoom.xSize && y < GravRoom.ySize) {
short type = engine.getRoom(engine.getCurrentRoom()).getGridPos(x,y);
if (type != 0) {
drawBlock(canvas, i, x, j, y, type);
}
}
}
private void drawBlock(Canvas canvas, int i, int x, int j, int y, short type) {
int left = i * scale, top = y * scale;
int right = left + scale;
int bot = top + scale;
paint.setColor(colorBlock(type));
canvas.drawRect(left, top, right, bot, paint);
System.err.println("Left" + left + " top: " + top + " right: "
+ right + " bot: " + bot);
}
private int colorBlock(short type) {
if (type == 1) {
return Color.DKGRAY;
} else if (type == 2) {
return Color.CYAN;
} else if (type == 3) {
return Color.GREEN;
} else if (type == 4) {
return Color.RED;
} else {
return Color.MAGENTA;
}
}
// private void imageBlock(short type) {
//
// }
}

Ouch !
Your call to your run method is executed in the UIThread (as the onCreate method), and it's doing an infinite loop in it.
Just add a println after the call and you will see that the UI thread is never released, your application should not even start !

You don't see any changes because you are creating a new canvas and drawing on that. To fix this, remove the line
canvas = new Canvas();
Also, you should initiate your Paint outside of the onDraw method (this is an optimization recommended by the Android documentation).

Collision detection using plain arrays and rectangles--java

I am almost done with my first little java game for my final project. It is a sidescroller where you have to shoot/avoid asteroids. My last problem is figuring out how to make my array of asteroids collide with the player's lasers. Here's what I have so far, there's an "AWT-EventQueue-0" java.lang.NullPointerException" on line 137, that I can't deal with. Any help is appreciated.
Edit: I added in my other classes, I realize it would be hard to judge the functionality of my code if I didn't show you where it came from.
package ShooterGame;
import java.applet.Applet;
import java.applet.AudioClip;
import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList;
import java.util.Random;
import javax.swing.*;
public class Board extends JPanel implements ActionListener
{
Enemy[] baddies = new Enemy[10000];
Player p;
Image img;
int y;
Timer time;
boolean lost = false;
static Font font = new Font("SanSerif", Font.BOLD, 24);
public AudioClip theme, bang, laser;
static ArrayList<Enemy> enemies;
public static int score = 0;
public static int lives = 5;
public Board()
{
p = new Player();
addKeyListener(new ActionListener());
setFocusable(true);
ImageIcon i = new ImageIcon("images/background.png");
img = i.getImage();
time = new Timer(5, this);
time.start();
for(int j = 0; j < baddies.length; j++)
{
Random ran = new Random();
y = ran.nextInt(365)+1;
baddies[j]= new Enemy((100*j + 700), y, "images/asteroid.gif");
}
theme = Applet.newAudioClip(getClass().getResource("theme.mid"));
theme.play();
bang = Applet.newAudioClip(getClass().getResource("bang.wav"));
}
public void actionPerformed(ActionEvent e)
{
checkCollisions();
ArrayList<?> bullets = Player.getBullets();
for(int i = 0; i < bullets.size(); i++)
{
Bullet b = (Bullet)bullets.get(i);
if(b.isVisible() == true)
{
b.move();
}
else
{
bullets.remove(i);
}
}
p.move();
for(int i = 0; i < baddies.length; i++)
{
if(p.x > 400)
{
baddies[i].move(p.getdx());
}
}
repaint();
}
public void paint(Graphics g)
{
super.paint(g);
Graphics2D g2d = (Graphics2D) g;
if(lost)
{
g2d.drawString("You Lose!", 300, 300);
}
if((p.getX() - 590) % 2400 == 0 || (p.getX() - 590) % 2400 == 1)
{
p.nx = 0;
}
if((p.getX() - 1790) % 2400 == 0 ||(p.getX() - 1790) % 2400 == 1)
{
p.nx2 = 0;
}
g2d.drawImage(img, 685-p.nx2, 0, null);
if(p.getX() >= 590)
{
g2d.drawImage(img, 685-p.nx, 0, null);
}
g2d.drawImage(p.getImage(), p.edge, p.getY(), null);
ArrayList<?> bullets = Player.getBullets();
for(int i = 0; i < bullets.size(); i++)
{
Bullet b = (Bullet)bullets.get(i);
g2d.drawImage(b.getImg(), b.getX(), b.getY(), null);
}
for(int i = 0; i < baddies.length; i++)
{
if(baddies[i].isAlive == true)
{
g2d.drawImage(baddies[i].getImg(), baddies[i].getX(), baddies[i].getY(), null);
}
}
g2d.setColor(Color.white);
g2d.drawString("Score: " + score, 0, 320);
g2d.drawString("Lives: " + lives, 80, 320);
}
public void checkCollisions()
{
Rectangle[] rect = new Rectangle[baddies.length];
for(int i = 0; i < baddies.length; i++)
{
Enemy e = (Enemy)baddies[i];
rect[i] = e.getBounds();
}
ArrayList<?> bullets = Player.getBullets();
for (int i = 0; i < bullets.size(); i++)
{
Bullet b = (Bullet) bullets.get(i);
Rectangle b1 = b.getBounds();
if (rect[i].intersects(b1) && baddies[i].isAlive())
{
score++;
baddies[i].isAlive = false;
baddies[i].isVisible = false;
bang.play();
}
Rectangle h = p.getBounds();
if (h.intersects(rect[i]))
{
if(baddies[i].isAlive() == true)
{
lives--;
if(lives < 0)
{
lost = true;
theme.stop();
System.exit(1);
}
}
}
}
}
private class ActionListener extends KeyAdapter
{
public void keyReleased(KeyEvent e)
{
p.keyReleased(e);
}
public void keyPressed(KeyEvent e)
{
p.keyPressed(e);
}
}
}
Enemy
package ShooterGame;
import java.awt.*;
import javax.swing.ImageIcon;
public class Enemy
{
int x, y;
Image img;
boolean isAlive = true;
boolean isVisible = true;
public Enemy(int startX, int startY, String location)
{
x = startX;
y = startY;
ImageIcon l = new ImageIcon(location);
img = l.getImage();
}
public Rectangle getBounds()
{
return new Rectangle(x, y, 60, 60);
}
public int getX()
{
return x;
}
public int getY()
{
return y;
}
public boolean isAlive()
{
return isAlive;
}
public boolean isVisible()
{
return isVisible;
}
public Image getImg()
{
return img;
}
public void move(int dx)
{
x = x - dx;
}
}
Bullet
package ShooterGame;
import java.applet.Applet;
import java.awt.*;
import javax.swing.ImageIcon;
import java.applet.AudioClip;
public class Bullet
{
int x, y;
Image img;
boolean visible;
public Bullet(int startX, int startY)
{
x = startX;
y = startY;
ImageIcon newBullet = new ImageIcon("images/bullet.gif");
img = newBullet.getImage();
visible = true;
}
public Rectangle getBounds()
{
return new Rectangle(x, y, 9, 5);
}
public int getX()
{
return x;
}
public int getY()
{
return y;
}
public Image getImg()
{
return img;
}
public boolean isVisible()
{
return visible;
}
public void move()
{
x = x + 2;
if(x > 700)
{
visible = false;
}
}
public void setVisible(boolean isVisible)
{
visible = isVisible;
}
}
Player
package ShooterGame;
import java.applet.Applet;
import java.applet.AudioClip;
import java.awt.*;
import java.awt.event.KeyEvent;
import java.util.ArrayList;
import javax.swing.ImageIcon;
public class Player
{
int x, dx, y, dy, nx2, nx, edge, ceiling;
Image player;
ImageIcon ib = new ImageIcon("images/player1back.gif");
ImageIcon i = new ImageIcon("images/playerstill.gif");
ImageIcon f = new ImageIcon("images/playerforward.gif");
ImageIcon up = new ImageIcon("images/playerup.gif");
ImageIcon down = new ImageIcon("images/playerdown.gif");
public AudioClip laser;
static ArrayList<Bullet> bullets;
public Player()
{laser = Applet.newAudioClip(getClass().getResource("laser.wav"));
player = ib.getImage();
x = 75;
nx = 0;
nx2 = 685;
y = 172;
edge = 150;
ceiling = 0;
bullets = new ArrayList<Bullet>();
}
public static ArrayList<Bullet> getBullets()
{
return bullets;
}
public void fire()
{
Bullet z = new Bullet((edge + 60), (y+17));
bullets.add(z);
}
public Rectangle getBounds()
{
return new Rectangle(edge, y, 43, 39);
}
public void move()
{
y = y + dy;
if(y < ceiling)
{
y = ceiling;
}
if(y > 290)
{
y = 290;
}
if(dx != -1)
{
if(edge + dx <= 151)
{
edge = edge + dx;
}
else
{
x = x + dx;
nx2 = nx2 + dx;
nx = nx + dx;
}
}
else
{
if(edge + dx > 0)
{
edge = edge + dx;
}
}
}
public int getX()
{
return x;
}
public int getdx()
{
return dx;
}
public int getY()
{
return y;
}
public Image getImage()
{
return player;
}
public void keyPressed(KeyEvent e)
{
int key = e.getKeyCode();
if(key == KeyEvent.VK_RIGHT)
{
dx = 2;
player = f.getImage();
}
if(key == KeyEvent.VK_UP)
{
dy = -1;
player = up.getImage();
}
if(key == KeyEvent.VK_DOWN)
{
dy = 1;
player = down.getImage();
}
if(key == KeyEvent.VK_SPACE)
{
fire();
laser.play();
}
}
public void keyReleased(KeyEvent e)
{
int key = e.getKeyCode();
if(key == KeyEvent.VK_RIGHT)
{
dx = 1;
player = ib.getImage();
}
if(key == KeyEvent.VK_UP)
{
dy = 0;
player = ib.getImage();
}
if(key == KeyEvent.VK_DOWN)
{
dy = 0;
player = ib.getImage();
}
}
}
Frame
package ShooterGame;
import javax.swing.*;
public class Frame
{
public AudioClip theme;
public Frame()
{
JFrame frame = new JFrame();
frame.add(new Board());
frame.setTitle("SideShooter");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(700,365);
frame.setVisible(true);
frame.setLocationRelativeTo(null);
}
public static void main(String[] args)
{
new Frame();
}
}

Ok, so the problem is the line mentioned in the other answer, but I believe it is that all the enemies may not be initialised before it checks collisions. Because you are making 10000 of them to start with, I think your action performed method may be checking collisions before they have all be created.
One thing to try could be to bring down the amount of enemies you have and see if it still keeps happening, try 100 or 1000, but this still won't fix the issue.
You really want to be change your game to run in it's own loop though, at the moment you are only checking collisions when the player performs an action. so if the player stops moving, no collision detection...
I would suggest that you find a book called 'Killer Game Programming in Java', there are free ebook version, and just read the first 2 chapters about making a game loop. The book is a bit old, but the basics of the loop are very good.
This question here also contains a very simple loop, and some suggestions in the comments about how to make it better.

The error is on the line
rect[i] = e.getBounds();
Are you not initializing the bounds of your Enemy class correctly? Alternatively, the Enemy you pulled out of the array could be null.