java GUI编程函数执行顺序问题

Question

import javax.swing.*;
import java.awt.*;
import java.io.IOException;
import gui.ZJM;
public class Bresenham extends JPanel {
private int x0;
private int y0;
private int xEnd;
private int yEnd;
private boolean temp=false;
void setyEnd(int i) {
// TODO 自动生成的方法存根
yEnd=i;
}

 void setxEnd(int i) {
    // TODO 自动生成的方法存根
    xEnd=i;
}

 void setY0(int i) {
    // TODO 自动生成的方法存根
    y0=i;
}

void setX0(int i) {
    // TODO 自动生成的方法存根
    x0=i;
}

//Graphics g=getGraphics();
@Override
public void paintComponent(Graphics g) {
    //super.paintComponent(g);

    Graphics2D g2d = (Graphics2D)g;

    g2d.translate(getWidth() / 2, getHeight() / 2);
    g2d.scale(1, -1); 
    g2d.drawLine(-400, 0, 400, 0);
    g2d.drawLine(0, -400, 0, 400);
    temp=true;

//g2d.drawLine(x0, y0, xEnd, yEnd);
//Bresline();

}
public void setPixel(int x,int y){ 
    Graphics g = getGraphics();
     Graphics2D g2d = (Graphics2D)g;         
     g2d.translate(getWidth() / 2, getHeight() / 2);
     g2d.scale(1, -1); 
    g2d.setColor(Color.RED);
    g2d.fillOval(x,y,1,1);
      }
static void createAndShowGUI(Bresenham a) {
    JFrame frame = new JFrame();

    // Add your component.

    frame.setContentPane(a);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(700, 400);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
}
public void Bresline(){
    int dx=Math.abs(xEnd-x0),dy=Math.abs(yEnd-y0);
    int p=2*dy-dx;
    int twoDy=2*dy,twoDyMinusDx = 2*(dy-dx);
    int x,y;

    if(x0>xEnd) {
        x=xEnd;
        y=yEnd;
        xEnd=x0;}
    else {
        x=x0;
        y=y0;
    }
    setPixel(x,y);
    while(x<xEnd) {
        x++;
        if(p<0)
            p+=twoDy;
        else {
            y++;
            p+=twoDyMinusDx;
        }
        setPixel(x,y);
        try {
             Thread.currentThread().sleep(250);
         }
         catch(Exception e){} 
    }

}
public void bresline(int x0,int y0,int xEnd,int yEnd) {
    Bresenham a = new Bresenham();
    a.setX0(x0);
    a.setY0(y0);
    a.setxEnd(xEnd);
    a.setyEnd(yEnd);
a.createAndShowGUI(a);
a.Bresline();
}
public static void main(String[] args) throws IOException {

}

}
问题1：为什么Bresline函数调用在画出坐标轴之前？
问题 2：如何修改才能在坐标轴上作图
补充：本意是想从另一个类中调用bresline（int，int，int，int）函数来实现作图，但测试的时候发现将x0，y0，yend，xend设为常数后从主函数调用bresline（）函数就对了

Answer 1

http://blog.csdn.net/u014492257/article/details/44505257