How Does Java's StringBuffer Reverse() Method Handle Surrogate Pairs in UTF-16 Encoding?

Surrogates in Java's UTF-16 Encoding

The StringBuffer class in Java provides a reverse() method that handles the reversal of Unicode characters, including surrogate pairs. Understanding surrogate pairs is crucial in this context.

What is a Surrogate Pair?

A surrogate pair is a mechanism used in the UTF-16 encoding scheme to represent Unicode characters with code points beyond 0xFFFF.

Internal UTF-16 Encoding

Java stores strings using UTF-16 encoding, which employs 16-bit (two-byte) code units. However, Unicode characters can have code points up to 0x10FFFF, which exceeds the capacity of UTF-16.

Surrogates for High Code-Points

Surrogates are used to encode these high code-points. They come in two ranges:

• High Surrogates: Code units ranging from 0xD800 to 0xDBFF, indicating the start of a surrogate pair.
• Low Surrogates: Code units ranging from 0xDC00 to 0xDFFF, indicating the end of a surrogate pair.

A surrogate pair is formed by combining a high surrogate with a low surrogate. This allows for a total range of 65,536 (2^16) high code-points.

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