Java字节基元类型是否有任何实际用途？ [英] Are there any real life uses for the Java byte primitive type?

问题描述

出于某种莫名其妙的原因， byte 原语类型是用Java签名的。这意味着有效值为-128..127而不是通常的0..255范围，表示一个字节中的8个有效位（没有符号位）。

For some inexplicable reason the byte primitive type is signed in Java. This mean that valid values are -128..127 instead of the usual 0..255 range representing 8 significant bits in a byte (without a sign bit).

这意味着所有字节操作代码通常进行整数计算并最终屏蔽掉最后8位。

This mean that all byte manipulation code usually does integer calculations and end up masking out the last 8 bits.

我想知道是否有任何真实生活场景中Java byte 原始类型是否完全适合，或者它只是一个完全无用的设计决策？

I was wondering if there is any real life scenario where the Java byte primitive type fits perfectly or if it is simply a completely useless design decision?

编辑：唯一的实际用例是本机代码的单字节占位符。换句话说，不要被操作为Java代码中的字节。

The sole actual use case was a single-byte placeholder for native code. In other words, not to be manipulated as a byte inside Java code.

编辑：我现在看到一个地方一个内部紧密循环需要除以7（数字0..32），因此可以使用字节作为数据类型来完成查找表，这样可以保持较低的内存使用率，考虑L1缓存的使用。这不是指签名/无签名，而是实际使用情况。

I have now seen a place where an inner tight loop needed to divide by 7 (numbers 0..32) so a lookup table could be done with bytes as the datatype so the memory usage could be kept low thinking of L1 cache usage. This does not refer to the signed/unsignedness but was a case of an actual usage.

推荐答案

令人惊讶的是，我只是用<$上周第一次在Java中使用c $ c> byte ，所以我确实有一个（尽管是不寻常的）用例。我正在编写一个本机Java函数，它允许您在可以调用的库中实现一个函数通过Java。需要将Java类型转换为本机语言中的类型，在本例中为C

Amazingly, I just used byte in Java for the first time last week, so I do have an (albeit unusual) use-case. I was writing a native Java function, which lets you implement a function in a library that can be called by Java. Java types need to be converted to types in the native language, in this case C

获取字节数组所需的函数，但是（忘记了 byte 当时完全输入）我需要一个 char [] 。为C函数生成的签名Java将该参数的类型赋予 jcharArray ，它可以转换为一堆 jchar s，在 jni.h 中的类型定义为 unsigned short 。当然，这不是相同的大小 - 它是2个字节而不是1.这导致了底层代码的各种问题。使Java类型 byte [] 产生 jbyteArray ，并且 jbyte 是typedef-ed到 signed char ，这是正确的大小

The function needed to take an array of bytes, but (forgetting about the byte type entirely at the time) I had it take a char[]. The signature Java generates for the C function gives the type of that parameter as jcharArray, which can be converted to a bunch of jchars, which are typedef-ed in jni.h to unsigned short. Naturally, that is not the same size -- it's 2 bytes instead of 1. This caused all sorts of problems with the underlying code. Making the Java type byte[] resulted in a jbyteArray, and jbyte on Linux is typedef-ed to signed char, which is the right size

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