Java で 数当てゲーム

Main.java

import java.io.*;

public class Main {
  static int small = 1;
  static int big   = 100;

  private static int guessMyNumber() {
    return (small + big) / 2;
  }

  private static int smaller() {
    big = guessMyNumber() - 1;
    return guessMyNumber();
  }

  private static int bigger() {
    small = guessMyNumber() + 1;
    return guessMyNumber();
  }

  public static void main(String[] args) throws IOException {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    boolean isFinish = false;
    String mes;
    while (!isFinish) {
      mes = in.readLine();
      switch (mes) {
        case "smaller":
          System.out.println(smaller());
          break;
        case "bigger":
          System.out.println(bigger());
          break;
        case "yes":
          System.out.println("Yeah! Thank you playing!");
          isFinish = true;
          break;
        default:
          System.out.println(guessMyNumber());
      }
    }
  }
}