What is the Java's internal represention for String? Modified UTF-8? UTF-16?

Question

I searched Java's internal representation for String, but I've got two materials which look reliable but inconsistent.

One is:

http://www.codeguru.com/cpp/misc/misc/multi-lingualsupport/article.php/c10451

and it says:

Java uses UTF-16 for the internal text representation and supports a non-standard modification of UTF-8 for string serialization.

The other is:

http://en.wikipedia.org/wiki/UTF-8#Modified_UTF-8

and it says:

Tcl also uses the same modified UTF-8[25] as Java for internal representation of Unicode data, but uses strict CESU-8 for external data.

Modified UTF-8? Or UTF-16? Which one is correct? And how many bytes does Java use for a char in memory?

Please let me know which one is correct and how many bytes it uses.

Answer 1

Java uses UTF-16 for the internal text representation

The representation for String and StringBuilder etc in Java is UTF-16

https://docs.oracle.com/javase/8/docs/technotes/guides/intl/overview.html

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.

http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html

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?

A char is always two bytes, if you ignore the need for padding in an Object.

Note: a code point (which allows character > 65535) can use one or two characters, i.e. 2 or 4 bytes.