为什么字节的总和是整数? [英] Why is the sum of bytes integer?

问题描述

我有 tyo 字节变量

I have tyo byte variable

byte a = 3;
byte b = 4;

如果我把它们相加，sum的值是整数.

If I sum them, the value of sum is integer.

byte z = a+b  //error, left side is byte, right side is integer

为什么 a+b 是 int?

Why a+b is int?

推荐答案

因为Java 语言规范 这么说

对操作数执行二进制数字提升(第 5.6.2 节).

Binary numeric promotion is performed on the operands (§5.6.2).

注意二进制数值提升执行值集转换(§5.1.13) 并且可以执行拆箱转换 (§5.1.8).

Note that binary numeric promotion performs value set conversion (§5.1.13) and may perform unboxing conversion (§5.1.8).

数字操作数上的加法表达式的类型是提升的其操作数的类型.

The type of an additive expression on numeric operands is the promoted type of its operands.

并且，关于数字推广,

加宽基元转换(第 5.1.2 节)用于转换或两个操作数均由以下规则指定:

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

• [...]
• 否则，两个操作数都转换为int类型.

所以 byte 值被提升为 int 值并相加.表达式的结果是提升的类型，因此是 int.

So the byte values are promoted to int values and added up. The result of the expression is the promoted type, therefore an int.

你可以简单地转换结果

byte z = (byte) (b + a);

但要小心溢出/下溢.

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