Java char数组是否始终是有效的UTF

Java char数组是否始终是有效的UTF-16（Big Endian）编码？(Is a Java char array always a valid UTF-16 (Big Endian) encoding?)

假设我将Java字符数组（ char[] ）实例编码为字节：

每个字符使用两个字节 使用大端编码（在最左边的最左边存储最高8位，在最右边的字节存储最不重要的8位）

这总是会创建一个有效的UTF-16BE编码吗？ 如果不是，哪些代码点会导致无效的编码？

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这个问题与这个关于Java字符类型和关于Java字符串内部表示的问题有很大关系。

Say that I would encode a Java character array (char[]) instance as bytes:

using two bytes for each character using big endian encoding (storing the most significant 8 bits in the leftmost and the least significant 8 bits in the rightmost byte)

Would this always create a valid UTF-16BE encoding? If not, which code points will result in an invalid encoding?

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This question is very much related to this question about the Java char type and this question about the internal representation of Java strings.

最满意答案

不可以。您可以创建包含您需要的任何16位值的char实例 - 没有任何内容将它们限制为有效的UTF-16代码单元，也不会将它们的数组限制为有效的UTF-16序列。 即使String不要求其数据是有效的UTF-16：

char data[] = {'\uD800', 'b', 'c'}; // Unpaired lead surrogate String str = new String(data);

有效的UTF-16数据要求在Unicode标准的第3章中列出（基本上，所有内容必须是Unicode标量值，所有代理必须正确配对）。 您可以测试char数组是否是有效的UTF-16序列，并使用CharsetEncoder将其转换为UTF-16BE（或LE）字节CharsetEncoder ：

CharsetEncoder encoder = Charset.forName("UTF-16BE").newEncoder(); ByteBuffer bytes = encoder.encode(CharBuffer.wrap(data)); // throws MalformedInputException

（如果你有字节，也可以使用CharsetDecoder 。）

No. You can create char instances that contain any 16-bit value you desire---there is nothing that constrains them to be valid UTF-16 code units, nor constrains an array of them to be a valid UTF-16 sequence. Even String does not require that its data be valid UTF-16:

char data[] = {'\uD800', 'b', 'c'}; // Unpaired lead surrogate String str = new String(data);

The requirements for valid UTF-16 data are set out in Chapter 3 of the Unicode Standard (basically, everything must be a Unicode scalar value, and all surrogates must be correctly paired). You can test if a char array is a valid UTF-16 sequence, and turn it into a sequence of UTF-16BE (or LE) bytes, by using a CharsetEncoder:

CharsetEncoder encoder = Charset.forName("UTF-16BE").newEncoder(); ByteBuffer bytes = encoder.encode(CharBuffer.wrap(data)); // throws MalformedInputException

(And similarly using a CharsetDecoder if you have bytes.)