java update scheduler可以禁用吗 java update needed

如例题

importjava.awt.*;importjava.awt.event.*;classMyCanvasextendsCanvasimplementsMouseListener{intleft=-1,right=-1;intx=-1,y=-1;MyCanvas(){setSize(200,200);setBackground...

如例题

import java.awt.*;
import java.awt.event.*;
class MyCanvas extends Canvas implements MouseListener
{
int left=-1,right=-1;
int x=-1,y=-1;
MyCanvas()
{
setSize(200,200);
setBackground(Color.pink);
addMouseListener(this);
}
public void paint(Graphics g)
{
if(left==1)
{
g.drawString("●",x,y);
}
else if(right==1)
{
g.drawString("○",x,y);
}
}
public void mousePressed (MouseEvent e)
{
x=e.getX();
y=e.getY();
if(e.getModifiers()==InputEvent.BUTTON1_MASK)
{
left=1;
right=-1;
repaint();
}
else if(e.getModifiers()==InputEvent.BUTTON3_MASK)
{
right=1;
left=-1;
repaint();
}
}
public void mouseReleased(MouseEvent e){}
public void mouseEntered(MouseEvent e){}
public void mouseExited(MouseEvent e)
{
left=-1;
right=-1;
repaint();
}
public void mouseClicked(MouseEvent e){}
public void update(Graphics g)
{
if(left==1||right==1)
{
paint(g);
}
else
{
super.update(g);
}
}
}
public class Shubiaoshijian
{
public static void main(String args[])
{
Frame f=new Frame();
f.setBounds(100,100,300,300);
f.setVisible(true);
f.addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent e)
{
System.exit(0);
}
});
f.setLayout(new FlowLayout());
f.add(new MyCanvas());
f.validate();
}
}
中的这一部分
public void update(Graphics g)
{
if(left==1||right==1)
{
paint(g);
}
else
{
super.update(g);
}
}
super.update

详细介绍下到底是什么用处的作用

因为这个地方导致整个程序有些不解