String methods

[sree visu]

Please help me to teach the replace that takes three arguments.Is this mock question correct

what will be the outputs of the following code

    
A. String s = "123456789"
S. = (s-"123").replace (1,3, "24") - "89";
 

B. StringBuffer s = new StringBuffer ("123456789"); S.delete (0,3) replace(1,3,"24"). Delete (4,6)
 
C. StringBuffer s = new StringBuffer ("123456789"); S.substring (3,6).delete(1,3). insert (1, "24").
 
D. StringBuilder s \= new StringBuilder ("123456789"); S.substring (3,6) delete (1,2). insert (1, "24")
 
E. StringBuilder s = new StringBuilder ("123456789"); S.delete (0,3) replace(1,3,). Delete (2,5) insert (1, "24")
Answer: B,
 

[Panseer Kaur]

Why not stick it in the compiler and see what it does?

[Sergey Petunin]

A is incorrect because you cannot use the "-" operator on strings, and also the replace method for strings has a different syntax.
B is correct. The replace method for StringBuffer takes three arguments. Here's the method prototype:
StringBuffer replace (int start, int end, String str)
start is the starting character index, end - 1 is the last character index, str is a string to substitute instead of the denoted characters.
So after s.delete(0,3) the StringBuffer has "456789", after .replace(1,3,"24") - "424789", after .delete(4,6) - "4247".
C and D is incorrect because the substring method returns an object of type String which does not have a delete method, so the method chaining fails here.
E is incorrect because the replace method in StringBuilder takes 3 arguments.