PlasticDimwittedCable created by max_l - https://repl.it/@max_l/PlasticDimwittedCable

Main.java

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Random;

import javax.swing.ButtonGroup;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.SwingUtilities;

/*
 * Basic geometric shape with an X,Y position
 * and an abstract draw method to be implemented
 * in subclasses. 
 * See:  https://docs.google.com/document/d/1Ng_W-_yeYQt8FLpdbquHXqdNUUjQjUDbGONPxOSAp60/edit#heading=h.hsuuk4b0auly
 */

abstract class Shape {

	private int x;
	private int y;

	public Shape(int x, int y) {
		this.setX(x);
		this.setY(y);
	}

	abstract public void draw(Graphics g);

	public int getX() {
		return x;
	}

	public void setX(int x) {
		this.x = x;
	}

	public int getY() {
		return y;
	}

	public void setY(int y) {
		this.y = y;
	}

	public String toString() {
		return "Shape(" + getX() + "," + getY() + ")";
	}
}

/*
 * The Insect class adds movement, it has an abstract move() method that updates
 * it's x,y coordinate to it's new position, and a abstract draw(Graphics2D)
 * method.
 * 
 * Subclasses will implement move() and draw().
 */

abstract class Insect extends Shape {

	protected double directionAngle;

	protected double speed = 2;

	protected Random randGen = new Random();

	private double randomAngle() {
		return randGen.nextFloat() * 2 * Math.PI;
	}

	public Insect(int x, int y) {
		super(x, y);
		directionAngle = randomAngle();
	}

	abstract public void move();

	// see: https://docs.oracle.com/javase/8/docs/api/java/awt/Graphics.html
	abstract public void draw(Graphics g);

}

class StraightLineMovingInsect extends Insect {

	public StraightLineMovingInsect(int x, int y) {
		super(x, y);
	}

	public void draw(Graphics g) {
		g.setColor(Color.RED);
		g.fillOval(getX(), getY(), 20, 20);
	}

	public void move() {

		double speed = 10;

		double deltaX = Math.cos(directionAngle) * speed;
		double deltaY = Math.sin(directionAngle) * speed;

		setX(getX() + ((int) deltaX));
		setY(getY() + ((int) deltaY));
	}
}

// class RandomAngleMovingInsect ...

class InsectSandboxPane extends JPanel {

	private int width;

	private int height;

	private ArrayList<Insect> shapes = new ArrayList<Insect>();

	public InsectSandboxPane(int width, int height) {
		this.width = width;
		this.height = height;
	}

	public Dimension getPreferredSize() {
		return new Dimension(width, height);
	}

	protected void paintComponent(Graphics g) {

		super.paintComponent(g);

		for (Shape s : shapes) {
			s.draw((Graphics2D) g);
		}
	}

	public void newInsect(Insect i) {
		shapes.add(i);
		this.repaint();
	}

	public void moveAll(MessageListener ml) {

		Iterator<Insect> ii = shapes.iterator();

		while (ii.hasNext()) {
			Insect s = ii.next();
			s.move();

			if (s.getX() >= width || s.getX() <= 0 || s.getY() >= height
			        || s.getY() <= 0) {
				ii.remove();
				String msg = "removed: " + s + ", " + shapes.size()
				        + " left in the sandbox !";
				System.out.println(msg);
				ml.newMessage(msg);
			}
		}

		this.repaint();
	}
}

interface MessageListener {
	public void newMessage(String msg);
}

class InsectSandBox extends JFrame {

	// Constants :

	private final int HEIGHT = 550;
	private final int WIDTH = 550;
	private final String straightLineInsect = "straightLineInsect";
	private final String randomAngleInsect = "randomAngleInsect";
	private final String randomAngleSpeedInsect = "randomAngleSpeedInsect";

	public InsectSandBox() {
		super("Sand Box");

		this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		this.setLayout(new BorderLayout());
		JPanel rootPanel = new JPanel(new BorderLayout());
		this.add(rootPanel);

		final InsectSandboxPane sandBox = new InsectSandboxPane(HEIGHT, WIDTH);
		rootPanel.add(sandBox, BorderLayout.CENTER);


		JPanel buttonPanel = new JPanel(new GridLayout(3, 1));

		rootPanel.add(buttonPanel, BorderLayout.SOUTH);

		JRadioButton b1 = new JRadioButton(straightLineInsect);
		b1.setActionCommand(straightLineInsect);
		JRadioButton b2 = new JRadioButton(randomAngleInsect);
		b2.setActionCommand(randomAngleInsect);
		JRadioButton b3 = new JRadioButton(randomAngleSpeedInsect);
		b3.setActionCommand(randomAngleSpeedInsect);

		final ButtonGroup buttonGroup = new ButtonGroup();
		buttonGroup.add(b1);
		buttonGroup.add(b2);
		buttonGroup.add(b3);

		JPanel radioPanel = new JPanel(new GridLayout(1, 3));
		buttonPanel.add(radioPanel);
		radioPanel.add(b1);
		radioPanel.add(b2);
		radioPanel.add(b3);

		b1.setSelected(true);

		final Random randGen = new Random();
		JButton newInsectButton = new JButton("new insect");
		buttonPanel.add(newInsectButton);

		// IMPORTANT: Anonymous Class, we create an anonymous ActionListener :
		// see:
		// https://docs.google.com/document/d/1Ng_W-_yeYQt8FLpdbquHXqdNUUjQjUDbGONPxOSAp60/edit#heading=h.bxqgrwqthxes

		newInsectButton.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent arg0) {

				String command = buttonGroup.getSelection().getActionCommand();

				if (command == straightLineInsect) {
					System.out.println("ADD straightWalker");

					sandBox.newInsect(new StraightLineMovingInsect(
					        (int) (randGen.nextFloat() * WIDTH), 
					        (int) (randGen.nextFloat() * HEIGHT)
					));
				} 
				else if (command == randomAngleInsect) {
					System.out.println("ADD randomAngleWalker");

					//sandBox.newInsect(new RandomAngleMovingInsect(
					//        (int) (randGen.nextFloat() * WIDTH), 
					//        (int) (randGen.nextFloat() * HEIGHT)
					//));					
				} 
				else if (command == randomAngleSpeedInsect) {
					System.out.println("ADD randomSpeedAngleWalker");

					//sandBox.newInsect(new RandomAngleAndSpeedMovingInsect(
					//        (int) (randGen.nextFloat() * WIDTH), 
					//        (int) (randGen.nextFloat() * HEIGHT)
					//));										                
				}
			}
		});

		this.pack();
		this.setVisible(true);

		final JLabel mesagesLabel = new JLabel("no messages yet");
		buttonPanel.add(mesagesLabel);

		// Other anonymous class:

		final MessageListener ml = new MessageListener() {
			public void newMessage(String msg) {
				mesagesLabel.setText(msg);
			}
		};

		// This is where the "moving" is triggered:

		Thread t = new Thread(new Runnable() {
			public void run() {
				while (true) {

					// Runs inside of the Swing UI thread
					SwingUtilities.invokeLater(new Runnable() {
						public void run() {
							sandBox.moveAll(ml);
						}
					});

					try {
						Thread.sleep(100); // sleep between moves
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}
			}

		});
		t.setDaemon(true);
		t.start();
	}
}

public class Main {

	public static void main(String[] args) throws Exception {

		InsectSandBox b = new InsectSandBox();
	}
}