String class provides the immutable character sequence whereas StringBuffer class objects are mutable characters sequence.
 The StringBuffer is faster than String when performing simple concatenations.
 Example:String s=new String(\"Hello\");s.toUpperCase();The String object s is still pointing to \"Hello\" instead  of \"HELLO\". Here a new string \"HELLO\" is created but did not assigned to any reference variable.But:StringBuffer sb=new StringBuffer(\"Hello\");sb.toUpperCase();The StringBuffer object sb is now pointing to the \"HELLO\".This is the main difference that string object are immutable and string buffer objects are mutable.

String class provides the immutable character sequence whereas StringBuffer class objects are mutable characters sequence.
 The StringBuffer is faster than String when performing simple concatenations.
 Example:String s=new String(\"Hello\");s.toUpperCase();The String object s is still pointing to \"Hello\" instead  of \"HELLO\". Here a new string \"HELLO\" is created but did not assigned to any reference variable.But:StringBuffer sb=new StringBuffer(\"Hello\");sb.toUpperCase();The StringBuffer object sb is now pointing to the \"HELLO\".This is the main difference that string object are immutable and string buffer objects are mutable.