//Lab3.java с главным классом программы
package lab3;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.Toolkit;
import javax.swing.JFrame;

/**
 *
 *
 */
public class Lab3 {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        JFrame frame = new JFrame("DrawTest");
        frame.setSize(new Dimension(600, 400));
        frame.setLocationRelativeTo(null);
        frame.setLayout(new GridBagLayout());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        GraphicsPanel graphicsPanel = new GraphicsPanel();

        frame.add(graphicsPanel, new GridBagConstraints(0, 0, 1, 1, 1.0, 1.0, GridBagConstraints.NORTH,
                GridBagConstraints.BOTH, new Insets(1, 1, 1, 1), 0, 0));

        frame.setVisible(true);


    }

//GraphicsPanel.java с классом, который предоставляет JPanel для рисования

package lab3;

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JPanel;

/**
 *
 *
 */
public class GraphicsPanel extends JPanel{

    @Override
    public void paintComponent(Graphics g) {
        Graphics2D gr = (Graphics2D)g;
        BasicStroke pen1 = new BasicStroke(5);
        gr.setStroke(pen1);

        for (int i = 0; i < 12; i++) {
             switch((int)Math.random()*2) {
                 case 0:
                     gr.setColor(new Color((int)Math.random()*255,(int)Math.random()*255, (int)Math.random()*255 ));
                     gr.drawLine(10, 20, 100, 50);
                     break;
                 case 1:
                     gr.setColor(new Color((int)Math.random()*255,(int)Math.random()*255, (int)Math.random()*255 ));
                     gr.drawRect(150, 50, 100, 50);
                     break;
                 case 2:
                     gr.setColor(new Color((int)Math.random()*255,(int)Math.random()*255, (int)Math.random()*255 ));
                     gr.drawOval(160, 90, 100, 50);
                     break;
             }
        }

    }
}