8-2 显示函数图像 (10 分)

Java 绘图，Graphics，JComponent类的使用以及重写paintComponent实现图像绘制

代码：

import javax.swing.*;
import java.awt.*;
import java.awt.geom.*;
class drawpic extends JComponent{
   private static final int W=600;     //组件大小
   private static final int H=800;
   public void paintComponent(Graphics g)    //重写本方法绘制组件形状
   {
      Graphics2D g2 = (Graphics2D)g;
      double xc=getWidth()/2;//中心点x
      double yc=getHeight()/2;//中心点y
      Line2D xz=new Line2D.Double();
      Line2D yz=new Line2D.Double();
      xz.setLine(0,yc,550,yc);
      yz.setLine(xc,50,xc,800);
      g2.draw(xz);
      g2.draw(yz);
      Line2D jt1=new Line2D.Double(),jt2=new Line2D.Double(),jt3=new Line2D.Double(),jt4=new Line2D.Double();
      jt1.setLine(550,yc,540,yc-10);
      jt2.setLine(550,yc,540,yc+10);
      g2.draw(jt1);g2.draw(jt2);
      jt3.setLine(xc,50,xc-10,60);
      jt4.setLine(xc,50,xc+10,60);
      g2.draw(jt3);g2.draw(jt4);
      g2.drawString("X",550,(int)(yc-15));
      g2.drawString("Y",(int)(xc+15),50);
      Polygon pl=new Polygon();
		double fac=0.05;     //让图像Y坐标成比例减小便于观看.
		for(int x=-200;x<=200;x++)
		{
			pl.addPoint((int)(x+xc),(int)(yc-x*x*fac));  //根据计算y坐标Y轴从上往下位置是从小到大
		}
		
		g.drawPolyline(pl.xpoints,pl.ypoints,pl.npoints);
   }

  public Dimension getPreferredSize()
  {
      return new Dimension(W,H);
   }
}
class mjf extends Jframe{
   public mjf(){
      add(new drawpic());
      pack();
   }
}
public class Main {
   public static void main(String[] args) {
      mjf jf=new mjf();
      jf.setDefaultCloseOperation(Jframe.EXIT_ON_CLOSE);
      jf.setTitle("f(x)=x^2函数图像的绘制");
      jf.setVisible(true);
   }
}