java - 变量 'menu' 可能尚未初始化

Question

我尝试制作一个使用 switch 和 do while 的菜单，但它返回:

variable 'menu' might not have been initialized

} while (menu != 5);

有人可以帮我吗？这是我的目标:

import java.util.Scanner;
  class HW {
    public static void main(String[] args) {
    Scanner entry = new Scanner(System.in);
    int A, B, X, menu; // there
    do {
      System.out.println("Main Menu");
      System.out.println("1.  Plus");
      System.out.println("2.  Minus");
      System.out.println("3.  Multiply");
      System.out.println("4.  Division");
      System.out.println("5.  Exit");
      System.out.println("Option :");
      X = entry.nextInt();
      switch (X) {
        case 1:
          System.out.println("Var A : ");
          A = entry.nextInt();
          System.out.println("Var B : ");
          B = entry.nextInt();
          System.out.println("Result : " + (A + B));
          if (A > B)
            System.out.println(A + ">" + B);
          else if (A == B)
            System.out.println(A + "=" + B);
          else if (A < B)
            System.out.println(A + "<" + B);
          System.out.println("*press any key back to menu*");
          menu = entry.nextInt(); // there
          break;
        case 2:
          System.out.println("Var A : ");
          A = entry.nextInt();
          System.out.println("Var B : ");
          B = entry.nextInt();
          System.out.println("Result : " + (A - B));
          if (A > B)
            System.out.println(A + ">" + B);
          else if (A == B)
            System.out.println(A + "=" + B);
          else if (A < B)
            System.out.println(A + "<" + B);
          System.out.println("*press any key back to menu*");
          menu = entry.nextInt(); //there
          break;
        case 3:
          System.out.println("Var A : ");
          A = entry.nextInt();
          System.out.println("Var B : ");
          B = entry.nextInt();
          System.out.println("Result : " + (A * B));
          if (A > B)
            System.out.println(A + ">" + B);
          else if (A == B)
            System.out.println(A + "=" + B);
          else if (A < B)
            System.out.println(A + "<" + B);
          System.out.println("*press any key back to menu*");
          menu = entry.nextInt(); //there
          break;
        case 4:
          System.out.println("Var A : ");
          A = entry.nextInt();
          System.out.println("Var B : ");
          B = entry.nextInt();
          System.out.println("Result : " + (A / B));
          if (A > B)
            System.out.println(A + ">" + B);
          else if (A == B)
            System.out.println(A + "=" + B);
          else if (A < B)
            System.out.println(A + "<" + B);
          System.out.println("*press any key back to menu*");
          menu = entry.nextInt(); //there
          break;
        case 5:
          break;
      }
    } while (menu != 5); //here it say not initialized.
    System.out.println(" ");
  }
}

Answer 1

您需要在最后一个case之后创建一个default语句。这是因为，如果没有一个情况属实，它仍然需要一个“后备计划”。它是 else 语句的对应部分。

在 case: 5 之后添加此内容:

default:
    menu = desiredNumberHere;
    break;