Regrading the Scanner object

[Ashwin Rao]

Here's the basic structure of my program till now:

import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner choice = new Scanner(System.in);
int select = choice.nextInt();
if(select == 1){
if(choice.hasNextByte())
switch(choice.nextByte()){
case 1: //do stuff
case 2: //do stuff
case 3: //do stuff
default: //do some more stuff
}
}
else if(select == 2) {
String input = new String();
choice = new Scanner(System.in);
/* If I comment out this line the program doesn't
* wait for my input at all! I'm not able to understand
* why that's happening!
*/
input = choice.nextLine();
input = input.trim();
//more stuff follows
}
}
}

On line 23: Why doesn't the 'choice' work with existing Scanner object?
If I remove line 23 then the program doesn't wait for my input.
Any help is much appreciated!
Thanks in advance!!

[Dave Tolls]

This is down to the fact that nextLine() works differently to the other next() methods.
If you only want a single "word" (ie no spaces in the input) then use next(), otherwise you'll need to make two calls to nextLine().

The reason is that the regular nextXXX() methods read up to the next token (in the default Scanner that is a whitespace character, so space, tab, new line etc), they do no, however, read that character, so it is still in the buffer.

So reading in:
1
with nextInt() will leave a new line in the buffer.

Now, nextLine() reads in up to and including the next new line character (it discards the new line). So, after the above nextInt, if I then do a nextLine() it will read in that new line that has been left in the buffer, and return an empty String.

[Ashwin Rao]

Whoa! Mind blowing!! Thanks a lot!!

[Dave Tolls]

 

Ashwin Rao wrote:Whoa! Mind blowing!! Thanks a lot!!

I ought to keep that one in my past buffer, to be honest.

It comes up a lot, which (to me) implies a problem with how Scanner was designed.

[J. Kevin Robbins]

In fact, in comes up so often we have a couple of FAQs that address that very issue. Here and here.

[Campbell Ritchie]

 

Dave Tolls wrote:This is down to the fact that nextLine() works differently to the other next() methods. . . .

Or that people are not taught about it. I have yet to see a book with a good explanation of nextLine().

[Dave Tolls]

 

Campbell Ritchie wrote:

Dave Tolls wrote:This is down to the fact that nextLine() works differently to the other next() methods. . . .

Or that people are not taught about it. I have yet to see a book with a good explanation of nextLine().

I have yet to see a decent explanation of Scanner as a whole.
It just looks (to me) like it's been cobbled together.