The
term "surrogate pair" refers to a means of encoding Unicode
characters with high code-points in the UTF-16 encoding scheme.
In
the Unicode character encoding, characters are mapped to values
between 0x0 and 0x10FFFF.
Internally,
Java uses the UTF-16 encoding scheme to store strings of Unicode
text. In UTF-16, 16-bit (two-byte) code units are used. Since 16 bits
can only contain the range of characters from 0x0 to 0xFFFF, some
additional complexity is used to store values above this range
(0x10000 to 0x10FFFF). This is done using pairs of code units known
as surrogates.
The
surrogate code units are in two ranges known as "low surrogates"
and "high surrogates", depending on whether they are
allowed at the start or end of the two code unit sequence.
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