Java 中如何将整数转换为字节? [英] How are integers cast to bytes in Java?

问题描述

我知道 Java 不允许无符号类型，所以我想知道它如何将整数转换为字节.假设我有一个值为 255 的整数 a 并且我将整数转换为一个字节.该值是否以字节 11111111 表示?换句话说，该值是更多地被视为一个有符号的 8 位整数，还是只是直接复制整数的最后 8 位?

I know Java doesn't allow unsigned types, so I was wondering how it casts an integer to a byte. Say I have an integer a with a value of 255 and I cast the integer to a byte. Is the value represented in the byte 11111111? In other words, is the value treated more as a signed 8 bit integer, or does it just directly copy the last 8 bits of the integer?

推荐答案

这叫做 缩小原始转换.根据规范:

有符号整数到整数类型的缩窄转换 T 简单地丢弃了除 n 最低阶位之外的所有位，其中 n 是用于表示类型 T 的位数.除了可能丢失有关数值大小的信息之外，这还可能导致结果值的符号与输入值的符号不同.

A narrowing conversion of a signed integer to an integral type T simply discards all but the n lowest order bits, where n is the number of bits used to represent type T. In addition to a possible loss of information about the magnitude of the numeric value, this may cause the sign of the resulting value to differ from the sign of the input value.

所以这是您列出的第二个选项(直接复制最后 8 位).

So it's the second option you listed (directly copying the last 8 bits).

我不确定您的问题是否知道带符号的整数值是如何表示的，所以为了安全起见，我将指出 二进制补码 系统(Java 使用).

I am unsure from your question whether or not you are aware of how signed integral values are represented, so just to be safe I'll point out that the byte value 1111 1111 is equal to -1 in the two's complement system (which Java uses).

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