Java中字符的大小不是2字节吗?
时间：2023-07-28问题描述
我使用 RandomAccessFile 从文本文件中读取 byte.
I used RandomAccessFile to read a byte from a text file.
public static void readFile(RandomAccessFile fr) {
byte[] cbuff = new byte[1];
fr.read(cbuff,0,1);
System.out.println(new String(cbuff));
}
为什么我看到一个完整的字符被它读取?
Why am I seeing one full character being read by this?
推荐答案
一个char在Java中表示一个字符(*).它是 2 字节大(或 16 位).
A char represents a character in Java (*). It is 2 bytes large (or 16 bits).
这并不一定意味着一个字符的每个表示都是 2 个字节长.事实上，许多 字符编码 只为每个字符保留 1 个字节(或为最常见的字符保留 1 个字节)字符).
That doesn't necessarily mean that every representation of a character is 2 bytes long. In fact many character encodings only reserve 1 byte for every character (or use 1 byte for the most common characters).
当您调用 String(byte[]) 构造函数 你要求 Java 将 byte[] 转换为String 使用 平台的默认字符集.由于平台默认字符集通常是 1 字节编码(例如 ISO-8859-1)或可变长度编码(例如 UTF-8)，因此它可以轻松地将 1 字节转换为单个字符.
When you call the String(byte[]) constructor you ask Java to convert the byte[] to a String using the platform's default charset. Since the platform default charset is usually a 1-byte encoding such as ISO-8859-1 or a variable-length encoding such as UTF-8, it can easily convert that 1 byte to a single character.
如果您在使用 UTF-16(或 UTF-32 或 UCS-2 或 UCS-4 或 ...)作为平台默认编码的平台上运行该代码，那么您将不会得到有效的结果(您' 将获得一个包含 Unicode 替换字符的 String).
If you run that code on a platform that uses UTF-16 (or UTF-32 or UCS-2 or UCS-4 or ...) as the platform default encoding, then you will not get a valid result (you'll get a String containing the Unicode Replacement Character instead).
这就是您不应该依赖平台默认编码的原因之一:在 byte[] 和 char[]/String 或 InputStream 和 Reader 或 OutputStream 和 Writer 之间，你应该总是 指定您要使用的编码.如果您不这样做，那么您的代码将依赖于平台.
That's one of the reasons why you should not depend on the platform default encoding: when converting between byte[] and char[]/String or between InputStream and Reader or between OutputStream and Writer, you should always specify which encoding you want to use. If you don't, then your code will be platform-dependent.
(*) 不完全是:一个 char 代表一个 UTF-16 代码单元.一个或两个 UTF-16代码单元代表一个Unicode 代码点.一个 Unicode 码点通常代表一个字符，但有时多个 Unicode 码点用于组成一个字符.但是上面的近似值已经足够接近讨论手头的话题了.
(*) that's not entirely true: a char represents a UTF-16 code unit. Either one or two UTF-16 code units represent a Unicode code point. A Unicode code point usually represents a character, but sometimes multiple Unicode code points are used to make up a single character. But the approximation above is close enough to discuss the topic at hand.
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