Java uses UTF-16 for the internal text representation
The representation for String and StringBuilder etc in Java is UTF-16
How is text represented in the Java platform?
The Java programming language is based on the Unicode character set, and several libraries implement the Unicode standard. The primitive data type char in the Java programming language is an unsigned 16-bit integer that can represent a Unicode code point in the range U+0000 to U+FFFF, or the code units of UTF-16. The various types and classes in the Java platform that represent character sequences - char, implementations of java.lang.CharSequence (such as the String class), and implementations of java.text.CharacterIterator - are UTF-16 sequences.
At the JVM level, if you are using
-XX:+UseCompressedStrings (which is default for some updates of Java 6) The actual in-memory representation can be 8-bit, ISO-8859-1 but only for strings which do not need UTF-16 encoding.
and supports a non-standard modification of UTF-8 for string serialization.
Serialized Strings use UTF-8 by default.
And how many bytes does Java use for a char in memory?
char is always two bytes, if you ignore alignment issues (as most people do ;)
Note: a code point (which allows character > 65535) can use one or two characters, i.e. 2 or 4 bytes.