// The copyright of this program is reserved by 哲猫.
/* 
Leibniz 級数
*/ 

/* <applet code="Ex061009d.class" width=200 height=100> </applet> */

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

public class Ex061009d extends JApplet implements ActionListener{
  long num=0;
  JTextField tf;
  JLabel lb1,lb2;
	public void init(){
		Container cp = getContentPane();
		JPanel pl = new JPanel();
    pl.setLayout(null);
    pl.setBackground(Color.cyan);
    lb1 = new JLabel("項 数 = ");
    lb2 = new JLabel("πの近似値=");
    tf = new JTextField(10);
		lb1.setBounds(10,10,50,25);
		tf.setBounds(70,10,120,25);
		lb2.setBounds(10,60,190,25);
		tf.addActionListener(this);
		pl.add(lb1);
		pl.add(lb2);
		pl.add(tf);
		cp.add(pl);
	}
	
	public void actionPerformed(ActionEvent event){
		num = Long.valueOf(tf.getText()).longValue();
		lb2.setText("πの近似値= "+Leibniz(num));
	}
	
	public double Leibniz(long n){
		double val=0.0;
		int co = -1;
		for(long i=1;i<=n;i++){
			co=-1*co;
			val+=co/(2.0*i-1.0);
		}
		return(4.0*val);
	}
}