Exact difference between CharSequence and String i

Question

This question already has answers here:

CharSequence VS String in Java? (9 answers)

Why StringBuilder when there is String? (10 answers)

Choosing between CharSequence and String for an API [duplicate] (1 answer)

Closed 2 years ago.

I read this previous post. Can any one say what the exact difference between CharSequence and String is, other than the fact that String implements CharSequence and that String is a sequence of character? For example:

CharSequence obj = "hello";
String str = "hello";
System.out.println("output is : " + obj + "  " + str);

What happens when "hello" is assigned to obj and again to str ?

Answer 1

Consider UTF-8. In UTF-8 Unicode code points are built from one or more bytes. A class encapsulating a UTF-8 byte array can implement the CharSequence interface but is most decidedly not a String. Certainly you can't pass a UTF-8 byte array where a String is expected but you certainly can pass a UTF-8 wrapper class that implements CharSequence when the contract is relaxed to allow a CharSequence. On my project, I am developing a class called CBTF8Field (Compressed Binary Transfer Format - Eight Bit) to provide data compression for xml and am looking to use the CharSequence interface to implement conversions from CBTF8 byte arrays to/from character arrays (UTF-16) and byte arrays (UTF-8).

The reason I came here was to get a complete understanding of the subsequence contract.

Answer 2

From the Java API of CharSequence:

A CharSequence is a readable sequence of characters. This interface provides uniform, read-only access to many different kinds of character sequences.

This interface is then used by String, CharBuffer and StringBuffer to keep consistency for all method names.