Question

Since Java char is 16 bit long, I am wondering how can it represent the full unicode code point?
It can only represent 65536 code points, is that right?

Answer 1

Yes, a Java char is a UTF-16 code unit. If you need to represent Unicode characters outside the Basic Multilingual Plane, you need to use surrogate pairs within a java.lang.String. The String class provides various methods to work with full Unicode code points, such as codePointAt(index).

From section 3.1 of the Java Language Specification:

The Unicode standard was originally designed as a fixed-width 16-bit character encoding. It has since been changed to allow for characters whose representation requires more than 16 bits. The range of legal code points is now U+0000 to U+10FFFF, using the hexadecimal U+n notation. Characters whose code points are greater than U+FFFF are called supplementary characters. To represent the complete range of characters using only 16-bit units, the Unicode standard defines an encoding called UTF-16. In this encoding, supplementary characters are represented as pairs of 16-bit code units, the first from the high-surrogates range, (U+D800 to U+DBFF), the second from the low-surrogates range (U+DC00 to U+DFFF). For characters in the range U+0000 to U+FFFF, the values of code points and UTF-16 code units are the same.

The Java programming language represents text in sequences of 16-bit code units, using the UTF-16 encoding. A few APIs, primarily in the Character class, use 32-bit integers to represent code points as individual entities. The Java platform provides methods to convert between the two representations.

See the Character docs for more information.