填空题

本题是一个Applet，功能是用鼠标画不同颜色的图形。页面中有5个按钮“画红色图形”、“画绿色图形”、“画蓝色图形”、“橡皮”和“清除”，单击前三个按钮中的一个，按住鼠标左键或右键在面板中拖动，就能画出对应颜色的线条，单击“橡皮”按钮，按住鼠标左键或右键在面板中拖动就能将面板中的图形擦除掉，单击“清除”按钮，就能将面板中所有的图形清除掉。
import java. applet. * ;
import java. awt. * ;
import java. awt. event. * ;
public class java3 extends Applet implements ActionListener
int x-1, y=-l, rubberNote=0, clearNote=0;
Color c=new Color(255,0,0);
int con=3;
Button b_red, b_blue, b_green, b_clear, b_quit ;
public void init()

addMouseMotionListener(this);
b_red=new Button("画红色图形");
b_blue=new Button("画蓝色图形");
b_green=new Button("画绿色图形") ;
b_quit=new Button("橡皮");
bclear=new Button("清除");
add(b_red);
add(b_green);
add(b_blue);
add(b_quit);
add(b_clear);
b_red. addActionListener(this);
b_green. addActionListener(this);
b_blue. addActionListener(this);
b_quit. addActionListener(this);
b_clear. addActionListener(this);

public void paint()
if(x!=-1&&y!=-1&&rubberNote==0&&clearNote==0)
g. setColor(c);
g. fillOval(x, y, con, con);

else if(rubberNote==1&&clearNote==0)
g. clearRect(x, y, 10,10);

else if(clearNote==1&&rubberNote==0)
g. clearRect(0,0,getSize(). width, getSize().height);


public void mouseDragged(MouseEvent e)
x=(int) e. getX(); y=(int) e. getY(); repaint();

public void mouseMoved(MouseEvent e)
public void update(Graphics g)
paint(g);

public void actionPerformed(Event e)
if(e. getSource()==b_red)
rubberNote=0; clearNote=0; c=new Color(255,0,0);

else if(e. getSource()==b green)
rubberNote=0; clearNote=0; c=new Color(0,255,0);

else if(e. getSource()==b_blue)
rubberNote=0; clearNote=0; c=new Color(0,0,255);

if(e. getSource()==b_quit)
rubberNote=1; clearNote=0;

if(e. getSource()==b_clear)
clearNote=1; rubberNote=0; repaint();