java - 为什么我需要为 Integer 变量而不是 int 转换字符？

Question

为什么我需要在这里将字符转换为 int 类型:

Integer integer= (int) 'a';

但我不需要在这里转换:

int i='a';

Answer 1

根据 Java Language Specification 5.1.7. Boxing Conversion

Boxing conversion converts expressions of primitive type to corresponding expressions of reference type. Specifically, the following nine conversions are called the boxing conversions:

From type boolean to type Boolean

From type byte to type Byte

From type short to type Short

From type char to type Character

From type int to type Integer

From type long to type Long

From type float to type Float

From type double to type Double

From the null type to the null type

此规则是必要的，因为条件运算符 (§15.25) 将装箱转换应用于其操作数的类型，并将结果用于进一步的计算。