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

/* <applet code="Fact.class" width="300" height="50"> </applet> */

public class Factorial extends JApplet implements ActionListener {
  JTextField input;
  JLabel output;

  @Override
  public void init() {
    input=new JTextField("0", 8);
    output=new JLabel("   1");
    input.addActionListener(this);
    setLayout(new FlowLayout());
    add(input);  add(new JLabel("の階乗は")); 
    add(output); add(new JLabel("です。"));  
  }

  static int factorial(int n) { // factorial -- 階乗のこと
    int r = 1;
    for (; n>0; n--) {
      r *= n;  
    }
    return r;
  }
  
  public void actionPerformed(ActionEvent e) {
    try {
      int n = Integer.parseInt(input.getText());
      output.setText("  "+factorial(n));
    } catch (NumberFormatException ex) {
      input.setText("数値!");
    } 
  }
}