CurrentShape.java

public enum CurrentShape {
	SQUARE, 
	CIRCLE, 
	RECTANGLE, 
	NONE;
}

DrawStuff.java

import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.geom.Rectangle2D;
import java.awt.image.BufferedImage;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

@SuppressWarnings("serial")
public class DrawStuff extends JFrame implements MouseMotionListener, MouseListener, ActionListener{
	
	//shape sizes
	private static final int CANVAS_WIDTH = 800;
	private static final int CANVAS_HEIGHT = 500;
	private static final int CIRCLE_RADIUS = 150;
	private static final int RECTANGLE_HEIGHT = 150;
	private static final int RECTANGLE_WIDTH = 300;
	private static final int SQUARE_SIZE = 200;
	
	//shape numbers
	private CurrentShape currentShape = CurrentShape.NONE;
	private int currentX;
	private int currentY;
	
	//Canvas and panel declarations
	JPanel btnPanel;
	private BufferedImage canvasImage;
	private CanvasDrawArea canvas;
	
	
	public DrawStuff(){
		
		//set up buttons for shapes
		btnPanel = new JPanel(new FlowLayout());
		createButtons(btnPanel);
		
		//Create the drawing JPanel
		canvas = new CanvasDrawArea(); 
		canvas.setPreferredSize(new Dimension(CANVAS_WIDTH, CANVAS_HEIGHT));

		//set up image area
		canvasImage = new BufferedImage(CANVAS_WIDTH, CANVAS_HEIGHT, BufferedImage.TYPE_INT_ARGB);
		
		//set up window
		Container cp = getContentPane(); 
		cp.setLayout(new BorderLayout()); 
		cp.add(canvas, BorderLayout.CENTER); 
		cp.add(btnPanel, BorderLayout.SOUTH);
		
		//Sets up canvas (visible area)
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setTitle("Draw With Shapes!");
		pack();
		setVisible(true);
		requestFocus();
		
		//MyListener myListener = new MyListener();
		addMouseListener(this);
		addMouseMotionListener(this);
	}
	
	
	/**
	 * 
	 * Sets up the different buttons used 
	 * 
	 */
	private void createButtons(JPanel btnPanel){
		
		JButton btnSquare = new JButton("Square");
		btnPanel.add(btnSquare);
		btnSquare.addActionListener(this);
		
		JButton btnCircle = new JButton("Circle");
		btnPanel.add(btnCircle);
		btnCircle.addActionListener(this);
		
		final JButton btnRectangle = new JButton("Rectangle");
		btnPanel.add(btnRectangle);
		btnRectangle.addActionListener(this);
		
		final JButton btnClear = new JButton("Clear");
		btnPanel.add(btnClear);
		btnClear.addActionListener(this);
		
	}
	
	/**
	 * easy reset call
	 */
	public void reset(){
		repaint();
		requestFocus();
	}
	
	/**
	 * called every time a button is clicked
	 * sets up new shape for drawing
	 */
	@Override
	public void actionPerformed(ActionEvent ae){
		
		switch(ae.getActionCommand()){
			case "Square":
				currentShape = CurrentShape.SQUARE;
				break;
			case "Rectangle":
				currentShape = CurrentShape.RECTANGLE;
				break;
			case "Circle":
				currentShape = CurrentShape.CIRCLE;
				break;
			case "Clear":
			  //deletes old image and creates a new one
				canvasImage = new BufferedImage(canvas.getWidth(), canvas.getHeight(), BufferedImage.TYPE_4BYTE_ABGR);
				reset();
				currentShape = CurrentShape.NONE;
				break;
		}
	}
	
	
	class CanvasDrawArea extends JPanel{
		
		//maybe change to dynamic later?
		//shape colors
		private final Color CIRCLE_COLOR = Color.BLUE;
		private final Color RECTANGLE_COLOR = Color.RED;
		private final Color SQUARE_COLOR = Color.YELLOW;
		private final Color CANVAS_COLOR = Color.GREEN;
		
		@Override
		public void paintComponent(Graphics g){
			
			super.paintComponent(g);
			canvas.setBackground(CANVAS_COLOR);
			
			//uses a separate variable for graphics so they don't erase on each `paintComponent` call
			Graphics2D image = (Graphics2D) canvasImage.getGraphics();
			
			//larger border
			image.setStroke(new BasicStroke(3));
			
			//fills in the shape and then draws a border around it
			switch(currentShape){
				case RECTANGLE:
					Rectangle2D rect = new Rectangle2D.Double(currentX - (RECTANGLE_WIDTH / 2), 
							currentY - (RECTANGLE_HEIGHT / 2), RECTANGLE_WIDTH, RECTANGLE_HEIGHT);
					image.setColor(RECTANGLE_COLOR);
					image.fill(rect);
					image.setColor(Color.BLACK);
					image.draw(rect);
					break;
				case SQUARE:
					Rectangle2D rect1 = new Rectangle2D.Double(currentX - (SQUARE_SIZE / 2),
							currentY - (SQUARE_SIZE / 2), SQUARE_SIZE, SQUARE_SIZE);
					image.setColor(SQUARE_COLOR);
					image.fill(rect1);
					image.setColor(Color.BLACK);
					image.draw(rect1);
					break;
				case CIRCLE:
					image.setColor(CIRCLE_COLOR);
					image.fillOval(currentX - (CIRCLE_RADIUS / 2), currentY - (CIRCLE_RADIUS / 2), 
							CIRCLE_RADIUS, CIRCLE_RADIUS);
					image.setColor(Color.BLACK);
					image.drawOval(currentX - (CIRCLE_RADIUS / 2), currentY - (CIRCLE_RADIUS / 2), 
							CIRCLE_RADIUS, CIRCLE_RADIUS);
					break;
				default:
					
				}
			g.drawImage(canvasImage, 0, 0, null);
		}
	}
	
  /**
   * called each time the mouse button is released
   */
	@Override
	public void mouseReleased(MouseEvent e) {
		currentX = e.getX();
		currentY = e.getY() - 22; //the 22 is to account for the little exit button on the top
		reset();
	}
	
	@Override
	public void mouseDragged(MouseEvent e) {}

	@Override
	public void mouseMoved(MouseEvent e) {}

	@Override
	public void mouseClicked(MouseEvent e) {	}

	@Override
	public void mousePressed(MouseEvent e) {}

	@Override
	public void mouseEntered(MouseEvent e) {}

	@Override
	public void mouseExited(MouseEvent e) {}
	
}

Main.java

import javax.swing.SwingUtilities;

public class Main {
	public static void main(String[] args){
		SwingUtilities.invokeLater(new Runnable(){
			@Override
			public void run(){
				new DrawStuff();
			}
		});
	}
}