Java 14正式发布switch表达式特性。在之前的两个 Java 版本Java12，Java13，switch特性只是预览版。

新的switch表达式有助于避免一些bug，因为它的表达和组合方式更容易编写。

switch新的表达式有两个特点：支持箭头表达式返回。

支持yied和return返回值。

Java 14之前switch语法：switch (day) {

case MONDAY:

case FRIDAY:

case SUNDAY:

System.out.println(6);

break;

case TUESDAY:

System.out.println(7);

break;

case THURSDAY:

case SATURDAY:

System.out.println(8);

break;

case WEDNESDAY:

System.out.println(9);

break;

}

Java 14 switch表达式switch (day) {

case MONDAY, FRIDAY, SUNDAY -> System.out.println(6);

case TUESDAY -> System.out.println(7);

case THURSDAY, SATURDAY -> System.out.println(8);

case WEDNESDAY -> System.out.println(9);

}

Java 14的switch表达式使用箭头表达时，不需要我们在每一个case后都加上break，减少我们出错的机会。

Java14之前switch语法返回值int numLetters;

switch (day) {

case MONDAY:

case FRIDAY:

case SUNDAY:

numLetters = 6;

break;

case TUESDAY:

numLetters = 7;

break;

case THURSDAY:

case SATURDAY:

numLetters = 8;

break;

case WEDNESDAY:

numLetters = 9;

break;

default:

throw new IllegalStateException("Wat: " + day);

}

它不支持返回值，需要通过一个中间变量来返回。

Java14 switch表达式返回值int numLetters = switch (day) {

case MONDAY, FRIDAY, SUNDAY -> 6;

case TUESDAY -> 7;

case THURSDAY, SATURDAY -> 8;

case WEDNESDAY -> 9;

};

Java 14 Switch表达式使用yield返回值int j = switch (day) {

case MONDAY -> 0;

case TUESDAY -> 1;

default -> {

int d = day.toString().length();

int result = f(d);

yield result;

}

};