问答题

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 SketchPanel();
Container contentPane=getContentPane();
contentPane.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(int i=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 isShiftDnwn ())
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;