StringBuffer vs String

Question

I was asked a question. If you had to build an XML structure as text, would you use StringBuffer or String? I thought String is more efficient that StringBuffer, but some of my friends say StringBuffer is more efficient than String.

I assume, that StringBuffer is a class, where as String is a base datatype and StringBuffer would have some easy (wrapper) methods for String. So, it is an add-on to string. Which should make StringBuffer heavier than String. Then how come using StringBuffer better than String?

Answer 1

Your statement would have been true if the StringBuffer simply contains a string property and appends the value as string.
But that is not the case, basically there are two basic types/categories of objects based on their memory allocation behavior - Mutable and Immutable.

String is Immutable, which means every time you make a modification / concatenate text with existing text. The object is created newly by assigning new memory address and that is a very costly process.

Whereas StringBuffer on the other hand is Mutable, because of that the object is not created every time append is called.

Hope this helps.