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ChristianFrantz

thread error

139 posts in this topic

aha! created a new arraylist called BallREctangle

[source lang="java"]public ArrayList<Rectangle> BallRectangle;[/source]

then in the updategame method if loop...

[source lang="java"]BallRectangle.add(new Rectangle(newX, newY, 20, 20));[/source]

does this work for what i want?

scratch that

[source lang="java"] for(int i = 0; i < BALLS.size(); i++) {
BallRectangle.add(new Rectangle(BALLS.get(i).x, BALLS.get(i).y, 20, 20));[/source]

right below the checkCollision(); in the update game method

now i just need the for statement in my checkCollision method

after running my program with the new for loop it freezes when the first ball is created

this is in my checkcollision method

[source lang="java"] if(mainBallRectangle.intersects(BallRectangle.get(i)))
{
mainBall.xspeed = 0;
mainBall.yspeed = 0;
mainBall.xpos = 100;
mainBall.ypos = 100;
}[/source]

now the game doesnt even run lol Edited by burnt_casadilla
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[quote name='burnt_casadilla' timestamp='1345067697' post='4969958']
does this work for what i want?
[/quote]
That does work for what you want. It would probably be a little better design to use your getBallBounds method, but they get you the same results in this case.

[quote name='burnt_casadilla' timestamp='1345067697' post='4969958']
right below the checkCollision(); in the update game method
[/quote]
By doing this, you're making BallRectangle (variables should start with a lowercase letter ala ballRectangle) hold more and more rectangles. You're adding a new rectangle to it every time through the updateGame method (to get an idea of how often and fast that happens, add a debug statement at the beginning of the method that says something simple like "Running updateGame").

I think for the design approach you chose last night, a better approach is to go at it like you were earlier in that post.. add one rectangle every time you add one new ball.

Given what new code you've shown, I'm not sure why the program freezes without giving you any kind of error or anything. You'll have to show more code to get some thoughts on why that happens.
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[source lang="java"] public void updateGame()
{
long currentTime = System.currentTimeMillis();

long elapsedTime = currentTime - lastUpdateTime;

lastUpdateTime = currentTime;

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));
BallRectangle.add(new Rectangle(newX, newY, 20, 20));

timeSinceLastNewDot = 0;
}[/source]

ok restart lol. this adds a new rectangle every time a new ball is created

woops forgot to make a new arraylist in the init method

[source lang="java"]BallRectangle = new ArrayList<Rectangle>();[/source]

[source lang="java"] public ArrayList<Rectangle> BallRectangle;[/source]

what is the reason for needing both of the lines of code? how come just the first line wont work? Edited by burnt_casadilla
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[quote name='burnt_casadilla' timestamp='1345069996' post='4969975']
what is the reason for needing both of the lines of code? how come just the first line wont work?
[/quote]

Those 2 lines do 2 different things and you need both of them.

One of them ([i]public ArrayList BallRectangle;[/i]) declares your variable. It gives it an access modifier ([i]public[/i]), a data type ([i]ArrayList[/i]) and a name ([i]BallRectangle[/i]).
The other line ([i]BallRectangle = new ArrayList();[/i]) assigns a value to your variable. It constructs an object ([i]new ArrayList()[/i]) and then assigns the result of that statement (in this case, a newly reserved block of memory for an ArrayList) to the variable on the left side of the equal sign ([i]BallRectangle[/i]).

If you declared the variable and then tried to use it without assigning a value to it, the variable would have its default value. For data types that are [u]not[/u] primitive data types (primitive data types: [url="http://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html"]http://docs.oracle.c.../datatypes.html[/url]), that default value is null. This is where something should come full circle for you and register as something you've definitely seen before... If you try to call a method or access a field on a null object, you get a NullPointerException. I know you've seen that exception once or twice. And that process is the reason.
Declare: [i]public ArrayList ballList;[/i]
[s]Initialize/Assign: [i]ballList = new ArrayList();[/i][/s]
Use: [i]ballList.add(new Ball());[/i]

If you go straight from declaring to using, the Use line would throw a NullPointerException. Edited by j-locke
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well what do you know my program runs fine after adding that line. thanks for the explanation. i understand variable types, but i guess i didnt think about the arraylist as a variable.

[source lang="java"]public void checkCollision()
{
if(mainBallRectangle.intersects(fixedBallRectangle))
{
mainBall.xspeed = 0;
mainBall.yspeed = 0;
mainBall.xpos = 100;
mainBall.ypos = 100;
}

if(mainBallRectangle.intersects(BallRectangle.get(i)))
{
mainBall.xspeed = 0;
mainBall.yspeed = 0;
mainBall.xpos = 100;
mainBall.ypos = 100;
}[/source]

when i run the program with this it gives me an error. am i not calling the arraylist BallRectangle the right way?
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the error is at if(mainBallRectangle.intersects(BallRectangle.get(i)))

i is supposed to be the number of rectangles stored in the array BallRectangle. but now that i type it out it makes more sense to put that in a for loop

[source lang="java"]for(int i = 0; i < BallRectangle.size(); i++)
if(mainBallRectangle.intersects(BallRectangle.get(i)))
{
mainBall.xspeed = 0;
mainBall.yspeed = 0;
mainBall.xpos = 100;
mainBall.ypos = 100;
}[/source]

HOLY SHIT I WIN. Game complete :'D Edited by burnt_casadilla
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yay!!! now for snake lol

1. add a ball that deletes itself everytime mainBall intersects it. im just going to use fixedBallRectangle and mainBall for this.
2. somehow make the snake bigger... add another ball that follows the mainBall?

ok so i have one arraylist just to store the length of the snake. the rest should be relatively easy, drawing a new apple for the snake to eat and check collision and if the snake comes in contact with the apple i delete the apple and draw a new one at a random point

how do you remove an object drawn to the screen? Edited by burnt_casadilla
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Sounds like a strategy that can work. Good job setting up an approach of getting a little bit working then getting a little more working and so on.
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Awesome. Knock it out of the park! And feel free to make a thread to show off your work. Your fellow GameDevers enjoy trying out completed projects and throwing out (usually challenging) suggestions of other things to do/add.
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aw man one last question. i have a mainBall and a randomApple and im testing collision for them. every time i hit the randomApple with the mainBall it adds another main ball to my arrayList MainBall. The only problem is that it adds 4 balls to my mainball arraylist instead of just one. how do i fix that?

[source lang="java"]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 snake extends Applet implements Runnable
{
static final int WIDTH = 450; //set screen height
static final int HEIGHT = 450; // set screen width
private Image dbImage;
private Graphics dbg;

public ArrayList<Ball> SnakeSize;

static final int NUM_OF_BALLS = 4;

int i;
int t;

Rectangle randomAppleRectangle;
Rectangle BallRectangle;

Ball Ball = new Ball(100, 100, 10, 10, 0, 0);
Apple randomApple = new Apple(250, 250, 15, 15);

public void start()
{
Thread th = new Thread(this);
th.start();//start main game
}

public void updateGame()
{
randomAppleRectangle = getAppleBounds();
BallRectangle = getBallBounds();

checkCollision();

Ball.ypos += Ball.yspeed;
Ball.xpos += Ball.xspeed;

if (Ball.xpos < 1)
{
Ball.xpos = 449;
}

if (Ball.xpos > 449)
{
Ball.xpos = 1;
}
if (Ball.ypos < 1)
{
Ball.ypos = 449;
}

if (Ball.ypos > 449)
{
Ball.ypos = 1;
}

try
{
Thread.sleep(20);
}
catch(InterruptedException ex){}
}

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 class Ball
{
int width;
int height;
int xpos;
int ypos;
int xspeed;
int yspeed;

public Ball( int xpos, int ypos, int width, int height, int xspeed, int yspeed)
{
this.width = 10;
this.height = 10;
this.xpos = 100;
this.ypos = 100;
this.xspeed = 0;
this.yspeed = 0;
}

public void paintBall(Graphics g)
{
g.setColor(Color.black);
g.fillOval(Ball.xpos, Ball.ypos, width, height);
g.drawString(xpos + ", " + ypos, 20, 40);
}
}//mainBall

public class Apple
{
int x;
int y;
int width;
int height;

public Apple(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.red);
g.fillOval(x, y, width, height);
g.drawString("Apple printed at: " + randomApple.x + ", " + randomApple.y, 20, 60);
g.drawString("Size of snake: " + SnakeSize.size(), 20, 80);
} //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)
{
Ball.xspeed = -5;
Ball.yspeed = 0;
}

if(key == Event.RIGHT)
{
Ball.xspeed = 5;
Ball.yspeed = 0;
}

if(key == Event.UP)
{
Ball.yspeed = -5;
Ball.xspeed = 0;
}

if(key == Event.DOWN)
{
Ball.yspeed = 5;
Ball.xspeed = 0;
}
return true;
}

public void run()
{
while(true)
{
repaint();
}
}

public void init()
{
this.setSize(WIDTH, HEIGHT);

SnakeSize = new ArrayList<Ball>();

}

public void paint(Graphics g)
{
updateGame();

g.drawString("time: " + t, 20, 20);

Ball.paintBall(g);
randomApple.paint(g);
}

public Rectangle getBallBounds()
{
return new Rectangle(Ball.xpos, Ball.ypos, 10, 10);
}

public Rectangle getAppleBounds()
{
return new Rectangle(250, 250, 15, 15);
}

public void checkCollision()
{
if(BallRectangle.intersects(randomAppleRectangle))
{
SnakeSize.add(new Ball(Ball.xpos - 10, Ball.ypos - 10, 10, 10, 0, 0));
}
}
}[/source]
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I don't see where you're getting rid of the random apple after they collide. With that being the case, it seems very likely that the ball and apple are colliding so one gets added. Then next time through updateGame, they are still colliding so another gets added. And so on. If you get rid of that random apple after the collision(likely by making your one random apple be somewhere else), that should solve that.
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[source lang="java"]public void checkCollision()
{
if(BallRectangle.intersects(randomAppleRectangle))
{
randomApple = new Apple(randomNumber(), randomNumber(), 15, 15);

SnakeSize.add(new Ball(Ball.xpos - 10, Ball.ypos - 12, 12, 10, 0, 0));
}
}[/source]

perfect. once again, thank you so much :D
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