When a lot of changes are required in data which one you choose String or StringBuffer in java - The String type is a class in Java, it is used to represent a set of characters. Strings in Java are immutable, you cannot change the value of a String once
B.StringBuffers=newStringBuffer("123456789");s.delete(0,3).replace(1,3,"24").delete(4,6); C.StringBuffers=newStringBuffer("123456789");s.substring(3,6).delete(1,3).insert(1,"24"); D.StringBuilders=newStringBuilder("123456789");s.substring(3,6).delete(1,2).insert(1,"24"); ...