repaint()问题 查了好久没弄明白怎么回事

Question

import java.awt.BorderLayout;
import java.awt.Button;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
/**
 *
 * @author Administrator
 */
public class hua extends JFrame implements ActionListener{
    static hua frame=new hua();
    static Button button1=new Button("circle");
    static Button button2=new Button("ellipse");
   static JPanel pane=new JPanel();
    int circle=0;
    public static void main(String[] args) {
        frame.setTitle("简单的画图程序");
        frame.setSize(300, 250);
        frame.setLayout(new BorderLayout());
        frame.add(pane, BorderLayout.SOUTH);
        //frame.setBackground(Color.WHITE);
        pane.add(button1);
        pane.add(button2);
        button1.addActionListener(frame);
        button2.addActionListener(frame);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
    public void actionPerformed(ActionEvent e){
        Button button=(Button)e.getSource();
        if(button==button1){
            circle=1;
        }
        else
            circle=2;
        Graphics g=getGraphics();
        paint(g);
    }
   
    @Override
    public void paint(Graphics g){
        g.setFont(new Font("黑体",Font.ITALIC,20));
        g.setColor(Color.red);
        g.drawString("画圆或画椭圆", 120, 50);
        if(circle==1){
            /*g.setColor(Color.WHITE);
            g.drawOval(80, 60, 70, 120);
            g.setColor(Color.red);*/
            g.drawOval(100, 90, 70, 70);
            repaint();//此处repaint()怎么不起作用呢
        }
        else if(circle==2) {
            /*g.setColor(Color.WHITE);
            g.drawOval(100, 90, 70, 70);
            g.setColor(Color.red);*/
            g.drawOval(80, 60, 70, 120);
            repaint();//此处repaint()怎么不起作用呢
        }    }
}
想用repaint()实现，点画圆就画圆，然后点椭圆，然后画椭圆，圆消失，但是好像实现不了，不知为什么，还请各位帮忙解答一下   1.请告诉我一下为什么不能实现。2.怎么实现？  谢谢

Answer 1

import java.awt.BorderLayout;
import java.awt.Button;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
/**
 *
 * @author Administrator
 */
public class hua extends JFrame implements ActionListener{
    static hua frame=new hua();
    static Button button1=new Button("circle");
    static Button button2=new Button("ellipse");
   static JPanel pane=new JPanel();
    int circle=0;
    public static void main(String[] args) {
        frame.setTitle("简单的画图程序");
        frame.setSize(300, 250);
        frame.setLayout(new BorderLayout());
        frame.add(pane, BorderLayout.SOUTH);
        //frame.setBackground(Color.WHITE);
        pane.add(button1);
        pane.add(button2);
        button1.addActionListener(frame);
        button2.addActionListener(frame);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
    public void actionPerformed(ActionEvent e){
        Button button=(Button)e.getSource();
        if(button==button1){
            circle=1;
        }
        else
            circle=2;
        repaint();
    }
   
    @Override
    public void paint(Graphics g){
        super.paint(g);
        g.setFont(new Font("黑体",Font.ITALIC,20));
        g.setColor(Color.red);
        g.drawString("画圆或画椭圆", 120, 50);
        if(circle==1){
            /*g.setColor(Color.WHITE);
            g.drawOval(80, 60, 70, 120);
            g.setColor(Color.red);*/
            g.drawOval(100, 90, 70, 70);
        }
        else if(circle==2) {
            /*g.setColor(Color.WHITE);
            g.drawOval(100, 90, 70, 70);
            g.setColor(Color.red);*/
            g.drawOval(80, 60, 70, 120);
        }    }
}

Answer 2

public void actionPerformed(ActionEvent e){
        Button button=(Button)e.getSource();
        if(button==button1){
            circle=1;
        }
        else
            circle=2;
        /*Graphics g=getGraphics();
        paint(g);*/
        repaint();
    }public void paint(Graphics g){
        g.setFont(new Font("黑体",Font.ITALIC,20));
        g.setColor(Color.red);
        g.drawString("画圆或画椭圆", 120, 50);
        if(circle==1){
            /*g.setColor(Color.WHITE);
            g.drawOval(80, 60, 70, 120);
            g.setColor(Color.red);*/
            g.drawOval(100, 90, 70, 70);
            //repaint();//repaint call paint autoly
        }
        else if(circle==2) {
            /*g.setColor(Color.WHITE);
            g.drawOval(100, 90, 70, 70);
            g.setColor(Color.red);*/
            g.drawOval(80, 60, 70, 120);
            //repaint();//repaint call paint autoly
        }    }

Answer 3

repaint是外部需要重新画这个对象时用的，
repaint引起paint

Answer 4

版主点击了按钮，可是系统只有在第一次调用一次paint方法，后面你在点击就必须使用rapaint方法来重新让系统调用paint方法，达到你的目的。所有你的不行，你楼下的可以。