Java 14 - 开关表达式

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Java 12 向 Switch 语句引入了表达式，并将其作为预览功能发布。Java 13 添加了一个新的yield 构造来从 switch 语句返回值。在 Java 14 中，switch 表达式现在已成为一项标准功能。

• 每个 case 块都可以使用yield 语句返回一个值。

• 如果是枚举，则可以跳过默认情况。在其他情况下，需要默认情况。

例子

考虑以下示例 -

ApiTester.java

public class APITester {
   public static void main(String[] args) {
      System.out.println("Old Switch");
      System.out.println(getDayTypeOldStyle("Monday"));
      System.out.println(getDayTypeOldStyle("Saturday"));
      System.out.println(getDayTypeOldStyle(""));

      System.out.println("New Switch");
      System.out.println(getDayType("Monday"));
      System.out.println(getDayType("Saturday"));
      System.out.println(getDayType(""));
   }
   public static String getDayType(String day) {
      var result = switch (day) {
         case "Monday", "Tuesday", "Wednesday","Thursday", "Friday": yield "Weekday";
         case "Saturday", "Sunday": yield "Weekend";
         default: yield "Invalid day.";
      };
      return result;
   }
   public static String getDayTypeOldStyle(String day) {
      String result = null;
      switch (day) {
         case "Monday":
         case "Tuesday":
         case "Wednesday":
         case "Thursday":
         case "Friday":
            result = "Weekday";
            break;
         case "Saturday": 
         case "Sunday":
            result = "Weekend";
            break;
         default:
            result =  "Invalid day.";            
      }
      return result;
   }
}

编译并运行程序

$javac APITester.java
$java APITester

输出

Old Switch
Weekday
Weekend
Invalid day.
New Switch
Weekday
Weekend
Invalid day.