JAVA CODE

//Ex12_5 program
import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;

public class Ex12_5 extends Applet
             implements ActionListener
{
   private Label lbl;
   private TextField NumTxt;
   private int n;

   public void init()
   {
      lbl = new Label ("Enter value of n");
      add(lbl);

      NumTxt = new TextField(3);
      NumTxt.addActionListener(this);
      add(NumTxt);
   }
      
   public void paint (Graphics g)
   {
      int sum1 = 0, sum2 = 0;

      sum1 = (n * (n - 1)) / 2;

      for (int i = 1; i <= n; i++)
         sum2 = sum2 + i;

      g.drawString ("The sum of 1 to " + n + " using", 50, 50);
      g.drawString ("i)  formula  n(n - 1)/2  is " + sum1, 50, 70);
      g.drawString ("ii) normal loop is " + sum2, 50, 90);
   }

   public void actionPerformed (ActionEvent e)
   {
      n = Integer.parseInt (NumTxt.getText());
      repaint();
   }

}