Ниже приведена упрощенная, хотя и в равной степени функциональная обработка вашего кода с использованием подхода active , описанного в по ссылке, которую @camickr предоставил в комментариях .Эта реализация поддерживает ArrayList пользовательских Line объектов, которые можно использовать для воссоздания чертежа на repaint:
import java.awt.Graphics;
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JTextField;
import javax.swing.JButton;
import javax.swing.Box;
import javax.swing.JPanel;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import java.util.ArrayList;
// 1 - turtle up
// 2 - turtle down/draw
// 3 - turn right
// 4 - turn left
// 5 - move forward a number of steps
// 6 - display drawing
class Line {
int startX;
int startY;
int endX;
int endY;
Line(int startX, int startY, int endX, int endY)
{
this.startX = startX;
this.startY = startY;
this.endX = endX;
this.endY = endY;
}
}
public class TurtleGraphics2D extends JPanel implements ActionListener
{
private static final int FLOORSIZE = 400;
private static Box box;
private JTextField textField;
private JButton drawButton;
private int currentXPosition = 0;
private int currentYPosition = 0;
private int heading = 0; // initial heading is South
private boolean isDown = false; // to know when pen is up or down
private ArrayList<Line> lines = new ArrayList<>(); // a collection of lines to (re)draw
public TurtleGraphics2D()
{
box = Box.createVerticalBox();
textField = new JTextField("Enter Command...");
drawButton = new JButton("Display Drawing");
box.add(textField);
box.add(drawButton);
textField.addActionListener(this);
drawButton.addActionListener(this);
}
public void paintComponent(Graphics g)
{
super.paintComponent(g);
for (Line line: lines)
{
g.drawLine(line.startX, line.startY, line.endX, line.endY);
}
}
public void actionPerformed(ActionEvent event)
{
if (event.getSource() == textField)
{
try
{
int command = Integer.parseInt(textField.getText());
textField.setText("");
switch(command)
{
case 1:
isDown = false;
break;
case 2:
isDown = true;
break;
case 3: // right / clockwise
if (++heading > 3)
{
heading -= 4;
}
break;
case 4: // left / counterclockwise
if (--heading < 0)
{
heading += 4;
}
break;
case 5:
int steps = Integer.parseInt(JOptionPane.showInputDialog("Steps: "));
int prevX = currentXPosition;
int prevY = currentYPosition;
for (int i = 0; i < steps; i++)
{
if (heading == 0) // cursor South
{
// this condition ensures ArrayIndexOutOfBoundsException is avoided
if (++currentYPosition > FLOORSIZE)
{
currentYPosition--;
}
}
else if (heading == 1) // cursor West
{
if (--currentXPosition < 0)
{
currentXPosition++;
}
}
else if (heading == 2) // cursor North
{
if (--currentYPosition < 0)
{
currentYPosition++;
}
}
else if (heading == 3) // cursor East
{
if (++currentXPosition > FLOORSIZE)
{
currentXPosition--;
}
}
}
if (isDown)
{
lines.add(new Line(prevX, prevY, currentXPosition, currentYPosition));
}
break;
case 6:
repaint();
break;
default:
break;
}
}
catch(IllegalArgumentException ex)
{
JOptionPane.showMessageDialog(null, "Invalid Command", "Error Message", JOptionPane.ERROR_MESSAGE);
System.err.println("Invalid command");
}
}
else if (event.getSource() == drawButton)
{
repaint();
}
}
public static void main(String args[])
{
JFrame frame = new JFrame();
TurtleGraphics2D panel = new TurtleGraphics2D();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(500, 500);
frame.add(box, BorderLayout.NORTH);
frame.add(panel, BorderLayout.CENTER);
frame.setVisible(true);
}
}
Результат: 4 5 <150> 3 5 <150> 2 5 <50> 4 5 <50> 4 5 <50> 4 5 <50>