java - 类型转换值(value)和由此产生的数学

Question

short x, y; 
short z = ((short)x) + ((short)y); 

所以我了解到在 Java 中，一个值在相加时被认为是一个整数。这只是语言中的细微差别之一。但是，在这里，我已经将 short 转换为变量 x 和 y 并且它仍然给我一个错误提示

can't convert from int to short

Answer 1

so I understand that in java that a value is considered an integer when it is added.

不一定。如果您要添加 long 则不会s，例如。

However, here, I am already casting short to the variables x and y and it still gives me an error saying that can't convert from int to short.

那是因为您在添加值之前对其进行了转换； + 的结果仍然是 int . (事实上​​，(short)x 是一个空操作；x 是已经一个 short 。)

正确的写法是:

short z = (short)(x + y);

short我们晋升为 int s，加在一起，然后我们将结果向下转换为 short .

回复你的评论:

(I'm) not sure why first casting the x and the y to short and putting them into parentheses would not result in short + short addition

因为 Java 没有 short + short添加。它添加的最小尺寸是 int ，因为 the first thing “加法”运算符( + 和 - )做的是 binary numeric promotion :

1. If any operand is of a reference type, it is subjected to unboxing conversion (§5.1.8).

2. Widening primitive conversion (§5.1.2) is applied to convert either or both operands as specified by the following rules:

   • If either operand is of type double, the other is converted to double.

   • Otherwise, if either operand is of type float, the other is converted tofloat`.

   • Otherwise, if either operand is of type long, the other is converted to long.

   • Otherwise, both operands are converted to type int.

所以 short + short (或 char + char 或 byte + byte )变为 int + int屈服 int . Java 的唯一 整数加法是int + int => int和 long + long => long .