Java21 如何使用switch case

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1. Java8 和 Java21

Java8 引入字符串和枚举

Java21 可以返回值, yield关键字, switch 表达式, 模式匹配, null值处理

2. 代码案例

1. Java8

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public static void java8() {
       String day = "tuesday";
       switch (day) {
           case "monday":
               System.out.println("work");
               break;
           case "tuesday":
               System.out.println("work");
               break;
           case "saturday":
               System.out.println("day off");
               break;
           case "sunday":
               System.out.println("day off");
               break;
       }
        //枚举值monday,tuesday,wednesday,thursday,friday,saturday,sunday;
       Days days = Days.saturday;
       switch (days) {
           case Days.monday:
               System.out.println("work");
               break;
           case Days.tuesday:
               System.out.println("work");
               break;
           case Days.saturday:
               System.out.println("day off");
               break;
           case Days.sunday:
               System.out.println("day off");
               break;
       }
   }

运行结果

20240112010117
Java8运行结果

2. Java21

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public static String java21() {
       //null 处理
       var name = switch (getName()) {
           case "" -> "";
           case "1" -> "num";
           case null -> "null";
           default -> "unknown";
       };
       System.out.println(name);
       //模式匹配
       Object o = 1;
       Object a = switch (o) {
           case Integer i -> 1 + i;
           case String s -> "1" + s;
           default -> o.toString();
       };
       System.out.println(a);
       //yield ， 表达式
       String day = "sunday";
       return switch (day) {
           case "monday", "tuesday" -> "work";
           case "saturday", "sunday" -> {
               System.out.println("day off");
               yield "work";
           }
           default -> "unknown";
       };

   }

   static String getName() {
       return null;
   }

运行结果

java21运行结果