import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;
public class FibonacciSerial extends Applet implements ActionListener
{
  Label prompt = new Label("请输入菲波那契数列的长度(最大为10): ");
  TextField input = new TextField(5);
  String[] msg = new String[50];　　　　　　
  int RequireCnt = 0;
  int ReturnCnt = 0;

  public void init()
  {
    add(prompt);
    add(input);
    input.addActionListener(this);
    for(int i=0; i<50; i++)
      msg[i] = "";
  }

  public void paint(Graphics g )
  {
    for(int i = 0; i<RequireCnt + ReturnCnt +1; i++)
      g.drawString(msg[i],10, 40+15*i);
  }

  public void actionPerformed(ActionEvent e)
  {
    if(e.getSource() ==input)
    {
      RequireCnt = 0;
      ReturnCnt = 0;
      if(Integer.parseInt(input.getText()) > 10)
      {
        prompt.setText("Too Large!");
        input.setText("");
      }
      else
        Fibonacci(Integer.parseInt(input.getText()));
    }
    repaint();
  }

  long Fibonacci(int n)
  {
    long temp;

    RequireCnt ++;
    msg[RequireCnt + ReturnCnt] = Blanks(RequireCnt, ReturnCnt) +
      "Fibonacci(" + n + "):" ;
    if(n==0||n==1)
    {
      ReturnCnt ++;
      msg[RequireCnt + ReturnCnt] = Blanks(RequireCnt, ReturnCnt-1) +
        "Return" + n ;
      return n;
    }
    else
    {
      temp = Fibonacci(n-1) + Fibonacci(n-2);　　　//递归计算
      ReturnCnt ++;
      msg[RequireCnt + ReturnCnt] = Blanks(RequireCnt, ReturnCnt-1) +
        "Return" + temp ;
      return temp;
    }
  }

  String Blanks(int stepIn, int stepBack)
  {
    String blank= "";

    for(int i=0; i<(stepIn- stepBack); i++)
      blank = blank+"";
    return blank;
  }
  
}