对Swing的一点理解（一）

   最近几天学习Java_Swing的时候，用Java的2D画图的时候发现了一点问题，如果直接在JFrame中直接画图的话和容易就会出现下面的问题：

（因为我这里帖不上图片，所以把图片放在附件了大有需要看的，可以下载附件）
但是如果 在JFrame中加入一个JPanel 问题就没有了，这个问题我想有很多的初学者和我一样遇到过。加入JPanel以后的图：

（因为我这里帖不上图片，所以把图片放在附件了大有需要看的，可以下载附件）
<o:p></o:p>

这是他们的源代码：

java 代码

//这是第一幅图的代码

import javax.swing.*;
import java.awt.*;

public class Circle1 extends JFrame{
 public static void main(String[] args) {
 Circle1 Cir=new Circle1();

 }
 public Circle1(){
 super("Draw circle");
 setSize(500,500);
 setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 setVisible(true);
 }

public void paint(Graphics g)
{


int circlePointX=200;
int circlePointY=200;
int radius=200;

 int x = circlePointX;
 int y = circlePointY + radius;
 int d = 5 - 4 * radius;

 int deltaE = 12;
 int deltaSE = 20 - 8 * radius;//initialization.
g.drawRect(x,y,1,1);
g.drawRect(y,x,1,1);
g.drawRect(-y,x,1,1);
g.drawRect(-x,y,1,1);
g.drawRect(y,-x,1,1);
g.drawRect(x,-y,1,1);
g.drawRect(-x,-y,1,1);
g.drawRect(-y,-x,1,1);


 while ( y > x)
 {
 if (d <= 0)
 {
 d += deltaE;
 deltaSE += 8;
 }
 else
 {
 d += deltaSE;
 deltaSE += 16;
 y--;
 }

 deltaE += 8;
 x++;


 g.drawRect(x,y,1,1);
g.drawRect(y,x,1,1);
g.drawRect(-y,x,1,1);
g.drawRect(-x,y,1,1);
g.drawRect(y,-x,1,1);
g.drawRect(x,-y,1,1);
g.drawRect(-x,-y,1,1);
g.drawRect(-y,-x,1,1);;
 }
 }
 }

java 代码

//这是第二幅图的代码：

import javax.swing.*;
import java.awt.*;

public class Circle {
 public static void main(String[] args) {
 TestCircle Cir=new TestCircle();
 Cir.setVisible(true);
 Cir.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 }
}

class TestCircle extends JFrame{
 public TestCircle(){
 setTitle("Draw circle");
 setSize(500,500);
 DrawCirclePanel panel = new DrawCirclePanel();
 add(panel);
 }
}

class DrawCirclePanel extends JPanel{
 public void paint(Graphics g){
 int circlePointX=200;
 int circlePointY=200;
 int radius=200;

 int x = circlePointX;
 int y = circlePointY + radius;
 int d = 5 - 4 * radius;

 int deltaE = 12;
 int deltaSE = 20 - 8 * radius;//initialization.
 g.drawRect(x,y,1,1);
 g.drawRect(y,x,1,1);
 g.drawRect(-y,x,1,1);
 g.drawRect(-x,y,1,1);
 g.drawRect(y,-x,1,1);
 g.drawRect(x,-y,1,1);
 g.drawRect(-x,-y,1,1);
 g.drawRect(-y,-x,1,1);


 while ( y > x)
 {
 if (d <= 0)
 {
 d += deltaE;
 deltaSE += 8;
 }
 else
 {
 d += deltaSE;
 deltaSE += 16;
 y--;
 }

 deltaE += 8;
 x++;
 g.drawRect(x,y,1,1);
 g.drawRect(y,x,1,1);
 g.drawRect(-y,x,1,1);
 g.drawRect(-x,y,1,1);
 g.drawRect(y,-x,1,1);
 g.drawRect(x,-y,1,1);
 g.drawRect(-x,-y,1,1);
 g.drawRect(-y,-x,1,1);;
 }
 }
 }