Moving Statements Outside the Loop

There is no need to compute diameter for each iteration of the loop. The same for Y, the top edge of the squares. It is always the same. These two statments can be moved outside of the loop, as in the following version of the applet.

import javax.swing.JApplet;
import java.awt.*;

// Assume that the drawing area is 300 by 150.
// Draw ten red circles side-by-side across the drawing area.
public class TenCircles extends JApplet
{
  final int width = 300, height = 150;

  public void paint ( Graphics gr )
  { 
    gr.setColor( Color.red );
    int diameter = width/10;
    int Y = height/2 - diameter/2;    // the top edge of the squares

    int count =  0 ;
    while (  count < 10  )
    {
      int X = count*diameter;           // the left edge of each square
      gr.drawOval( X, Y, diameter, diameter );
      count = count + 1; 
    }

  }
}

This version is somewhat better than the previous version because needless computations are avoided. If a loop body is iterated millions of times (not unusual in a large programs) the program will run faster if some statements can be moved outside the loop.