In Java what is the difference between string vs stringbuffer ?

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

Strings are immutable . String buffer are mutable.
ie :

Once the String object is created it cannot be modified. Stringbuffer object can be modified.

String s = "abc"
s = s+""def" // a new string obect will either be created or assigned from string pool if exists.

StringBuffer st = new StringBuffer("abc");
st.append("def") ;// No new object is created st gets modified.