填空题 本题的功能是用键盘上的方向键来控制直线的绘制方向。如果一直按向上的方向键，则在窗口中从焦点开始向上缓慢绘制直线，按其他方向键也会向对应的方向缓慢地绘制直线，如果按下＜Shift＞键的话，绘制直线的速度会加快。
import java. awt. * ;
import java. awt. geom. * ;
import java. util. * ;
import java. awt. event. * ;
import javax. swing. * ;
public class java3
public static void main(String[] args)

SketchFrame frame=new SketchFrame();
frame. setDefaultCloseOperation(JFrame. EXIT_ON_CLOSE);
frame. show();

class SketchFrame extends JFrame

public SketchFrame()

setTitle("java3");
setSize (DEFAULT_WIDTH, DEFAULT_HEIGHT);
SketchPanel panel=new SketehPanel();
Container contentPane=getContentPane();
eontentPane, add(panel);

public static final int DEFAULT_WIDTH=300;
public static final int DEFAULT_ HEIGHT
=200;

class SketchPanel extends JPanel

public void sketchPanel()

last=new Point2D. Double(100,100);
lines=new ArrayList();
KeyHandler listener=new KeyHandler();
addkeyListener(this);
setFocusable(true);

public void add(int dx, int dy)

Point2D end=new Point2D. Double(last. getX()+dx,
last. getY()+dy);
Line2D line=new Line2D. Double(last, end);
lines, add(line);
repaint();
last=end;

public void paintComponent(Graphics g)

super. paintComponent(g);
Graphics2D g2=(Graphics2D)g;
for (inti=0; i＜lines, size(); i++)
g2. draw((Line2D) lines, get(i));

private Point2D last;
private ArrayList lines;
private static final int SMALL_ INCREMENT=1;
private static final int LARGE_ INCREMENT=5;
private class KeyHandler implements KeyListener

public void keyPressed(KeyEvent event)

KEY keyCode=event, getKeyCode();
int d;
if (event. isShiftDown())
d=LARGE_INCREMENT;
else
d=SMALL_INCREMENT;
if (keyCode==KeyEvent. VK_LEFT) add(-d,0);
else if (keyCode==KeyEvent. VK_RIGHT)add(d,0);
else if (keyCode==KeyEvent. VK_UP) add(0,-d);
else if (keyCode=KeyEvent. VK_DOWN)add(0,d) ;

public void keyReleased(KeyEvent event)
public void keyTyped(KeyEvent event)

char keyChar=event, getKeyChar();
int d;
if (Character. isUpperCase(keyChar))

d=LARGE_INCREMENT;
keyChar=Character. toLowerCase(keyChar);

else
d=SMALL_INCREMENT;