When BufferedReader and StringBuffer is used in java?

Answer 1

Buffered reader is just like Scanner, used to get user input.
StringBuffer is used for changeable strings

Answer 2

IO operations are always costlier .Rather than read one character at a time from the network or disk, the BufferedReader reads a large block at a time. That makes it faster. BufferedReader simply reads sequence of characters. StringBuffer is used to create mutable string. As you know String in Java is immutable.