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


public class EtchSketch 
{
	public static void main(String[] args)
	{
		JFrame frame = new JFrame();
		frame.setTitle("E-S Demo");
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		ESPanel panel = new ESPanel();
		panel.setFocusable(true);			// for the KeyListener to work, we have
		frame.add(panel);		//	to do this
		frame.setSize(300, 300);			// set the size of the frame
		frame.setVisible(true);
	}

	private static class ESPanel extends JPanel implements KeyListener
	{
		private boolean setClear;	// used to toggle whether to draw or erase screen
		private int x, y;			// the <x, y> cooridnate of the cursor
		private int direction;		// the latest direction the user has specified
									// 0 = left, 1 = up, 2 = right, 3 = down
		
		public ESPanel()
		{
			addKeyListener(this);
			setClear = false;			// do not erase unless user presses <Enter>
			x = 150;					// initialize the cursor position
			y = 150;
			direction = 0;				// initialize the direction to left
		}

		public void keyPressed(KeyEvent e) 		
		{
			switch(e.getKeyCode())		// upon key press, if it is an arrow key,
			{							// then set direction appropriately
				case KeyEvent.VK_LEFT: direction = 0; break;
				case KeyEvent.VK_UP: direction = 1; break;
				case KeyEvent.VK_RIGHT: direction = 2; break;
				case KeyEvent.VK_DOWN: direction = 3; break;
				case KeyEvent.VK_ENTER: 
				{						// if <Enter> then toggle boolean so that
					setClear = true;	// we can erase the screen
					break;
				}
			}
			repaint();
		}

		// implement the rest of the KeyListener
		public void keyTyped(KeyEvent e) {}
		public void keyReleased(KeyEvent e) {}

		public void paintComponent(Graphics g)
		{
			if(setClear)				// if the user wants to erase, then
			{							// erase g and reset boolean
				super.paintComponent(g);
				setClear = false;
			}
			else						// otherwise determine the direction and
			{							// draw a 2-pixel line in that direction
				g.setColor(Color.black);	// from the current position
				switch(direction)			// and then extend x or y appropriately
				{						// but stop at the "edge" of the screen (10 or 290)
					case 0 : g.drawLine(x, y, x-2, y); x-=2; if (x < 10) x = 10; break;
					case 1 : g.drawLine(x, y, x, y-2); y-=2; if (y < 10) y = 10; break;
					case 2 : g.drawLine(x, y, x+2, y); x+=2; if (x > 290) x = 290; break;
					case 3 : g.drawLine(x, y, x, y+2); y+=2; if (y > 290) y = 290; break;
				}
			}
		}
	}
}