java - 来自 UTF-16 编码的错误字节

Question

我有一个字符 '😭' Unicode 值是 U+1F62D 等效二进制是 11111011000101101 。现在我想将这个字符转换为字节数组。我的脚步

1) 由于二进制表示大于 2 个字节，我使用 4 个字节

XXXXXXXX XXXXXXX1 11110110 00101101

2) 现在我用“0”替换所有“X”

00000000 00000001 11110110 00101101

3) 十进制数

00000000(0) 00000001(1) 11110110(-10) 00101101(45)

这是我的代码

@Test
    public void testUtf16With4Bytes() throws Exception {
        assertThat(
                new String(
                        new byte[]{0,1,-10,45},
                        StandardCharsets.UTF_16BE
                ),
                is("😭")
        );
    }

这是输出

ava.lang.AssertionError: 
Expected: is "😭"
     but: was ""

我错过了什么？

Answer 1

您错过了一些 UTF 字符存储为 surrogate pairs :

In UTF-16, characters in ranges U+0000—U+D7FF and U+E000—U+FFFD are stored as a single 16 bits unit. Non-BMP characters (range U+10000—U+10FFFF) are stored as “surrogate pairs”, two 16 bits units: an high surrogate (in range U+D800—U+DBFF) followed by a low surrogate (in range U+DC00—U+DFFF). A lone surrogate character is invalid in UTF-16, surrogate characters are always written as pairs (high followed by low).

😭 字符是 U+1F62D 所以它属于 U+10000—U+10FFFF 范围。它用代理对 U+D83D U+DE2D 表示，如 byte[] 它将是 [-40, 61, -34, 45]。