import java.awt.*;
import java.awt.event.*;

public class MyFrame extends Frame implements WindowListener
{
TextField tfa;
TextField tfb;
Button b;
public MyFrame()
{
   setLayout(new BorderLayout());
  
   tfa=new TextField("输入正整数n",16);
   tfb=new TextField("结果s",16);
   b=new Button("计算");

   addWindowListener(this);
   b.addActionListener(new ButtonHandler());
  
   add(new Label("s=1/1+1/2+1/3+...1/n"),"North");
   add(tfa,"West");
   add(tfb,"East");
   add(b,"Center");

   setTitle("计算");
}
public static void main(String[] args)
{
   MyFrame fr=new MyFrame();
  
   fr.pack();
   fr.show();
}
class ButtonHandler implements ActionListener
{
   public void actionPerformed(ActionEvent e)
   {
    int n=Integer.parseInt(tfa.getText());//算法
    double sum=0;
    for(double j=1;j<=n;j++)
    {
     sum+=1/j;
    }
    tfb.setText(String.valueOf(sum));
   }
}
public void windowClosing(WindowEvent arg0) {
   System.exit(0);
}

public void windowActivated(WindowEvent arg0) {
   // TODO Auto-generated method stub
  
}

public void windowClosed(WindowEvent arg0) {
   // TODO Auto-generated method stub
  
}

public void windowDeactivated(WindowEvent arg0) {
   // TODO Auto-generated method stub
  
}

public void windowDeiconified(WindowEvent arg0) {
   // TODO Auto-generated method stub
  
}

public void windowIconified(WindowEvent arg0) {
   // TODO Auto-generated method stub
  
}

public void windowOpened(WindowEvent arg0) {
   // TODO Auto-generated method stub
  
}

}