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

/**
 * A Box has a visible appearance on screen as a square, white area.
 * A Box can contain a number of Balls, that can be moved around.
 */
class Box extends JComponent{

    private static final int MAXBALLS = 100;
    private static final int WIDTH = 400;
    private static final int HEIGHT= 400;
    private Ball [] theBalls;
    private int ballCount = 0;
    private Color color = Color.WHITE;

/**
 * Create an empty Box and render it on screen.
 */
    public Box(){
        theBalls = new Ball[100];
	setPreferredSize(new Dimension(WIDTH,HEIGHT));
    }

/**
 * Add a ball to this Box.
 */
    public void addBall(Ball b){
        theBalls[ballCount] = b;
        ballCount++;
    }

/**
 * Let each ball in the box do n steps, with
 * delay d milliseconds between each step.
 */
    public void moveAllBalls(int n, int d) {
        for(int k=0; k<n; k++) {
            for(int i = 0; i<ballCount; i++)
                theBalls[i].step();
            repaint();
            try{Thread.sleep(d);}
            catch(Exception e){}
        }
    }

    public void setColor(Color col) {
        color = col;
        repaint();
    }

    public void paint(Graphics g){
        Graphics2D g2 = (Graphics2D) g;
        g2.setColor(color);
        g2.fill(new Rectangle(0,0,WIDTH,HEIGHT));
        for(int i = 0; i<ballCount; i++){
            theBalls[i].paint(g);
        }
    }

}