Questions about the random squares again

Hi, here are the codes I got. I was wondering how do I put those yellow
squres inside the black rectangles? What am I missing?

//Description: Design and implement a class called Building that
represents a graphical depiction of a building. Allow the parameters to
the constructor to specify the building's width and height. Each
building should be colored black, and contain a few random windows of
yellow. Create a program that draws a random skyline of buildings.

import javax.swing.JFrame;
public class Building
{
    public static void main (String[] args)
    {
        JFrame frame = new JFrame ("Building");
        frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);

        frame.getContentPane().add(new BuildingPanel());

        frame.pack();
        frame.setVisible(true);
    }
}

//Building Panel
import javax.swing.*;
import java.awt.*;
import java.util.Random;

public class BuildingPanel extends JPanel
{
    private Rectangle rec1, rec2, rec3, rec4;
    private final int NUM_BOXES = 10;
    private final int X = 400, Y = 400;
    private Random generator;

    public BuildingPanel()
    {
        generator = new Random();
        rec1 = new Rectangle (40,190,Color.black,20,210);
        rec2 = new Rectangle (50,170,Color.black,90,230);
        rec3 = new Rectangle (70,215,Color.black,170,185);
        rec4 = new Rectangle (90,283,Color.black,310,117);

        setPreferredSize (new Dimension (400,400));
        setBackground (Color.blue);
    }
    public void paintComponent (Graphics page)
    {
        super.paintComponent(page);

        int x,y,width,height;

            rec1.draw(page);
            rec2.draw(page);
            rec3.draw(page);
            rec4.draw(page);

        for (int count=0; count< NUM_BOXES; count++)
        {
            x = generator.nextInt(X);
            y = generator.nextInt(Y);
            width = 8;
            height = 8;
            page.setColor (Color.yellow);
            page.fillRect (x, y, width, height);
        }

    }
}