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修正了文章中错误的原码、反码和补码，补充了byte & 0xFF中类型提升的细节 #180

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修正了文章中错误的原码、反码和补码，补充了byte & 0xFF中类型提升的细节 #180

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16 changes: 6 additions & 10 deletions docs/src/io/buffer.md
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Original file line number Diff line number Diff line change
Expand Up @@ -199,22 +199,24 @@ byte 类型是有符号的，即其取值范围为 -128 到 127。如果我们

& 运算是一种二进制数据的计算方式, 两个操作位都为1，结果才为1，否则结果为0. 在上面的 `getBufIfOpen()[pos++] & 0xff` 计算过程中, byte 有 8bit, OXFF 是16进制的255, 表示的是 int 类型, int 有 32bit.

Java中，byte类型参与运算时会自动提升为int类型，高位通过符号位扩展填充，正数补0，负数补1，byte & 0xFF会先将byte类型提升为int类型，然后将高24位置为0，去掉符号位的影响，仅保留低8位的原始值，从而得到原byte类型值的无符号整数值。

如果 `getBufIfOpen()[pos++]` 为 -118, 那么其原码表示为

```
00000000 00000000 00000000 10001010
10000000 00000000 00000000 01110110
```

反码为

```
11111111 11111111 11111111 11110101
11111111 11111111 11111111 10001001
```

补码为

```
11111111 11111111 11111111 11110110
11111111 11111111 11111111 10001010
```

0XFF 表示16进制的数据255, 原码, 反码, 补码都是一样的, 其二进制数据为
Expand All @@ -225,12 +227,6 @@ byte 类型是有符号的，即其取值范围为 -128 到 127。如果我们

0XFF 和 -118 进行&运算后结果为

```
00000000 00000000 00000000 11110110
```

还原为原码后为

```
00000000 00000000 00000000 10001010
```
Expand Down Expand Up @@ -449,4 +445,4 @@ GitHub 上标星 10000+ 的开源知识库《[二哥的 Java 进阶之路](https

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