# JEP 420：简化的 switch 表达式
---
Java 14 引入了 `switch` 表达式， Java 18 实现了 `JEP 420`
以下是 `switch` 表达式
```Java
int numLetters = switch (day) {
case MONDAY, FRIDAY, SUNDAY -> 6;
case TUESDAY -> 7;
case THURSDAY, SATURDAY -> 8;
case WEDNESDAY -> 9;
default -> 11;
};
```
### 对比
之前
```Java
static String formatter(Object o) {
String formatted = "unknown";
if (o instanceof Integer i) {
formatted = String.format("int %d", i);
} else if (o instanceof Long l) {
formatted = String.format("long %d", l);
} else if (o instanceof Double d) {
formatted = String.format("double %f", d);
} else if (o instanceof String s) {
formatted = String.format("String %s", s);
}
return formatted;
}
```
之后
```Java
static String formatterPatternSwitch(Object o) {
return switch (o) {
case Integer i -> String.format("int %d", i);
case Long l -> String.format("long %d", l);
case Double d -> String.format("double %f", d);
case String s -> String.format("String %s", s);
default -> o.toString();
};
}
```
对于简短的 `switch` 逻辑，可以更加清晰的表达
