Why is getHeight() not equal to the frame height?

Question

I am making a bounc*ing cube that moves around a frame. To detect the boundary of the frame, I used getHeight() and getWidth() from the JComponent in the JFrame and calculate the possible boundary so that the cube can rebound.

It works totally fine for getWidth(). However, I cannot make it rebound on the boundary for getHeight().

When the cu*be goes to the top of the window, it keeps going for about 10 pixels before rebounding.

Here is the screenshot for this problem.

enter image description here

Here is my code:

public class Cube {
    final public static int DIMENSION = 100;
    private final static int D_X = 20;
    private final static int D_Y = -20;
    private final static int SPEED = 1;
    private int xVelBK;
    private int yVelBK;
    private int xVel;
    private int yVel;
    private CubePoint[] pts;

    public  Cube(int x, int y){
    xVel = SPEED;
    yVel = SPEED;

    pts = new CubePoint[8];

    pts[0] = new CubePoint(x,y);
    pts[1] = new CubePoint(x,y - DIMENSION);
    pts[2] = new CubePoint(x + DIMENSION,y - DIMENSION);
    pts[3] = new CubePoint(x + DIMENSION,y);

    pts[4] = new CubePoint(x + D_X,y + D_Y);
    pts[5] = new CubePoint(x + D_X,y + D_Y - DIMENSION);
    pts[6] = new CubePoint(x + D_X + DIMENSION,y + D_Y - DIMENSION);
    pts[7] = new CubePoint(x + D_X + DIMENSION,y + D_Y);
    }

    public void move(int componentWidth, int componentHeight){
    ......

    //bug in here
    if (pts[0].getY()  - DIMENSION - D_Y <= 0 ) {
        yVel = SPEED;
    }

    .......
    }
..........
}

Here is the component :

public class CubeComponent extends JComponent {
    ...........

    private Cube cube;
    private Timer timer;
    private CubePoint originMousePos;
    private CubePoint closest;
    private Font font;
    private int mode;


    private int delay = DEFAULT_DELAY ;

    private int mouseToClosestX;
    private int mouseToClosestY;

    class CubeMoveListener implements ActionListener{
    @Override
    public void actionPerformed(ActionEvent e){
        cube.move(getWidth(),getHeight());
        repaint();
    }

    }



    @Override
    public void paintComponent(Graphics g){
    Graphics2D g2 = (Graphics2D)g;

    cube.draw(g2);
    }

}

The window title is included in the window's size. There's a function that tells you the size of the "inside part" of the window, but I don't remember what it's called right now. (Someone else might) — user253751, Mar 09 '15 at 03:56
`public void paintComponent(Graphics g){ ..` should be `public void paintComponent(Graphics g){ super.paintComponent(g); ..` (for the 5th time today). — Andrew Thompson, Mar 09 '15 at 04:11
possible duplicate of [JFrame : Getting actual content size](http://stackoverflow.com/questions/7154633/jframe-getting-actual-content-size) — fdsa, Mar 09 '15 at 04:16

score 4 · Accepted Answer · answered Mar 09 '15 at 04:22

As far as I can tell:

 if (pts[0].getY()  - DIMENSION - D_Y <= 0 ) {

SHOULD be used to determine when the cube reaches the bottom of the component so you should be testing for ">"

and

if ( pts[0].getY() >= componentHeight) {

SHOULD be used for testing when the cube reaches the top. So it should be:

if ( pts[0].getY() <= 0) {

The key point is that:

ONE of the vertical tests needs to test for "<= 0".
the structure of the horizontal and vertical test should be the same, you just need to change the variable names.

Why is getHeight() not equal to the frame height?

1 Answers1