String Vs StringBuffer Vs StringBuilder

String is immutable while StringBuffer and StringBuilder is mutable object.

StringBuffer is synchronized while StringBuilder is not which makes StringBuilder faster than StringBuffer.

Concatenation operator "+" is internal implemented using either StringBuffer or StringBuilder.

Criteria to choose among String, StringBuffer and StringBuilder(Simple)

          Use String if you require immutability, 
          Use Stringbuffer in java if you need mutable + threadsafety 
          Use StringBuilder in Java if you require mutable + without thread-safety.

Criteria to choose among String, StringBuffer and StringBuilder(Explained in detail)

          If your text is not going to change use a string Class because a String object is immutable        

          If your text can change and will only be accessed from a single thread, use a StringBuilder because StringBuilder is unsynchronized.

          If your text can changes, and will be accessed from multiple threads, use a StringBuffer because StringBuffer is synchronous.