Question

I’m in computer SCI AP and I can’t figure out why this isn’t working

public static void moon(Graphics g) {
    for(int k = 0; k < 550; k+=2) {
        if (k == 550) {     
            g.setColor(Color.blue);
            g.fillOval(k,50,50,50);
            for(long delay = 1; delay<10000000; delay++);   
            g.setColor(Color.white);
            g.fillOval(k,50,50,50); 
            k = 0;
        } else {
            g.setColor(Color.black);
            g.fillOval(k,50,50,50);
            for(long delay = 1; delay<10000000; delay++);   
            g.setColor(Color.white);
            g.fillOval(k,50,50,50); 
        }
    }
}

So basically is will make the black oval move across the screen then when k = 550 it will make the blue one go across the screen.. But it doesn’t do that it just moves the black one then after it hits 550 it stops.. and the blue one doesn’t come up.

Answer 1

Your code never reaches k = 550.
The condition in the for loop is k < 550. Make it k <= 550 and it should work.

However, you may not see it happen, because you’re using for(long delay = 1; delay<10000000; delay++); to delay – this is not a very reliable way to delay.

To see things happen more reliably, try using Thread.sleep(long).
For the record, I believe there are some arguments against using Thread.sleep(long) in general, but in this case it should suffice.

While I’m at it, the k = 0 assignment is superfluous, it’s even bad style. You should not assign to a loop variable inside the loop. If the loop is entered again, the for (int k=0 part will take care of setting k to 0.

HTH