JAVA问题,谢谢!

算PI值？

pi=4-4/3+4/5-4/7+4/9-4/11+.......

此方法在三百步后才取到3.14的近似值
import java.applet.Applet;
import java.awt.Graphics;
import java.awt.*;
public class Pi extends Applet{

public void init(){
resize(1400,1000);
}

public void paint(Graphics g){
int i;
int x=25,y=25;
for(int m=1;m<=300;m++){
double pi=0.0,l=1.0;
for(i=0;i<=m;i++){
pi+=(double)(4.0/(i*2.0+1.0))*l;
l*=-1.0;
}
g.drawString(pi+"",x,y);
y+=10;
if(m%80==0)
{x+=200;
y=25;}
}
}
}