能否在switch case中使用逻辑或(||)？求优化月份天数计算代码

原始代码 #

Scanner keyboard = new Scanner(System.in);
out.print("Enter month : ");
String month = keyboard.nextLine().toLowerCase();
switch (month){
    case "january" :
        out.println("31 days");
        break;

    case "february" :
        out.println("");
        out.print("Is it a leap year (yes/no): ");
        String leap_year = keyboard.nextLine().toLowerCase();
        if (leap_year.equals("no")){
            out.println("28 days");
            break;
        } if (leap_year.equals("yes")){
            out.println("29 days");
            break;  
        } else{
            out.println("Invalid option.. Use yes/no only.");
            break;
        }
        
    case "march" :
        out.println("31 days");
        break;
    case "april" :
        out.println("30 days");
        break;

    case "may" :
        out.println("31 days");
        break;
    case "june" :
        out.println("30 days");
        break;

    case "july" :
        out.println("31 days");
        break;

    case "august" :
        out.println("31 days");
        break;

    case "september" :
        out.println("30 days");
        break;

    case "october" :
        out.println("31 days");
        break;

    case "november" :
        out.println("30 days");
        break;

    case "december" :
        out.println("31 days");
        break;
    default :
        out.println("Enter a correct month");
        break;

}
keyboard.close();

用Switch多Case简化代码（替代逻辑或） #

Java 7及以上支持字符串类型的Switch，并且允许将多个case合并，把天数相同的月份放在一起，直接减少重复代码：

Scanner keyboard = new Scanner(System.in);
out.print("Enter month : ");
String month = keyboard.nextLine().toLowerCase();

switch (month) {
    case "january":
    case "march":
    case "may":
    case "july":
    case "august":
    case "october":
    case "december":
        out.println("31 days");
        break;
    case "april":
    case "june":
    case "september":
    case "november":
        out.println("30 days");
        break;
    case "february":
        out.print("Is it a leap year (yes/no): ");
        String leapYearInput = keyboard.nextLine().toLowerCase();
        if ("no".equals(leapYearInput)) {
            out.println("28 days");
        } else if ("yes".equals(leapYearInput)) {
            out.println("29 days");
        } else {
            out.println("Invalid option.. Use yes/no only.");
        }
        break;
    default:
        out.println("Enter a correct month");
        break;
}
keyboard.close();

其他优化建议 #

• 提取闰年判断逻辑为独立方法：把二月的闰年判断抽成单独方法，让主逻辑更简洁，也方便复用：

  private static void printFebruaryDays(Scanner scanner, PrintStream out) {
      out.print("Is it a leap year (yes/no): ");
      String input = scanner.nextLine().toLowerCase();
      switch (input) {
          case "yes":
              out.println("29 days");
              break;
          case "no":
              out.println("28 days");
              break;
          default:
              out.println("Invalid option.. Use yes/no only.");
      }
  }
  

  主代码里直接调用这个方法即可。

• 使用枚举类管理月份：用枚举存储月份名称和天数（二月特殊处理），增强类型安全，避免字符串输入的潜在错误：

  enum Month {
      JANUARY(31),
      FEBRUARY(28),
      MARCH(31),
      APRIL(30),
      MAY(31),
      JUNE(30),
      JULY(31),
      AUGUST(31),
      SEPTEMBER(30),
      OCTOBER(31),
      NOVEMBER(30),
      DECEMBER(31);
  
      private final int days;
  
      Month(int days) {
          this.days = days;
      }
  
      public int getDays(boolean isLeapYear) {
          if (this == FEBRUARY && isLeapYear) {
              return 29;
          }
          return days;
      }
  }
  

  之后可以通过Month.valueOf(month.toUpperCase())获取枚举实例，再调用方法获取天数。

• 循环校验输入合法性：对于月份和闰年的输入，如果用户输入错误，循环提示直到输入正确，提升用户体验。

• 支持数字月份输入：允许用户输入1-12的数字，再映射到对应月份，增加程序的灵活性。

内容的提问来源于stack exchange，提问作者Yashwant Balaji