Why cant I simply check if a variable is null instead of checking for different exceptions?

Question

Consider this, if userChoice is not an integer:

Scanner choice = new Scanner(System.in);
int userChoice = choice.nextInt();
if(....){
    .... //not important
}
else if(userChoice == null){
    System.out.println("wrong input..");
    System.exit(0);
}

Why cant I do this? And instead have to do:

import java.util.InputMismatchException;

..... //bunch of code

Scanner choice = new Scanner(System.in);
    int userChoice;
    try {
        userChoise = choice.nextInt();
        if(...){
          ..... //not important
        }
    }
    catch(InputMismatchException e) {
        System.out.println("wrong input..");
        System.exit(0);
    }

I thought it was so that if I inputed, say, a char when it expected an int it would simply return null. So if I checked for null then it would be sufficient. So what am I missing/not understading?

So this is not a question regarding the Scanner library. If you want to boil it down it was that I did not know that a integer could not be null. So the user who thought that this was duplicated, it might be. But it is certainly not a duplicate to the post that you suggested..

Scanner Class throws Exception on input mismatch instead `null` which an `int` can not be — Sanjeev, Jun 29 '16 at 12:51
This may be useful: http://stackoverflow.com/q/970029/423955 Java primitive types cannot be null. Only references to Objects can be null. — Alessandro Da Rugna, Jun 29 '16 at 12:51
Possible duplicate of [Validating input using java.util.Scanner](http://stackoverflow.com/questions/3059333/validating-input-using-java-util-scanner) — Tom, Jun 29 '16 at 12:55

Shiro · Answer 1 · 2016-06-29T13:05:53.400

4

An int cannot be null. It can be any number in its range.

edited Jun 29 '16 at 13:05

answered Jun 29 '16 at 12:50

Shiro

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2

Please be more precise: an `int` cannot be null; an `Integer` can; `integer` is not a thing in Java. – Andy Turner Jun 29 '16 at 13:02
I did say integer not `Integer` and int is short for: integer. – Shiro Jun 29 '16 at 13:03
@AndyTurner I thought an `int` was short for `integer`? – Felix Rosén Jun 29 '16 at 13:04
@Shiro So ther is a diffrence bewteen `integer` and `Integer` ?!??!! – Felix Rosén Jun 29 '16 at 13:05
2

@FelixRosén obviously it is; but by saying "integer", it is not clear whether you are referring to `Integer` (which can be null) or `int` (which cannot be null). – Andy Turner Jun 29 '16 at 13:05
Are you happy now? – Shiro Jun 29 '16 at 13:06
@AndyTurner So ther is a diffrence bewteen `integer` and `Integer` ?? – Felix Rosén Jun 29 '16 at 13:06
1

@FelixRosén Have a look at this: https://docs.oracle.com/javase/7/docs/api/java/lang/Integer.html – Shiro Jun 29 '16 at 13:07
1

@FelixRosén yes. `Integer` usually refers to `java.lang.Integer`; `integer` is not a standard type in Java. – Andy Turner Jun 29 '16 at 13:08
@Shiro yes. Thanks. – Andy Turner Jun 29 '16 at 13:19

score 0 · Answer 2 · answered Jun 29 '16 at 12:52

Apart from the fact that you need to use Integer instead of int if you want to return null, it is not advisable. The main reason is that checking an output for null is easily forgotten and may lead to error situations much later in the program.

An exception, though, has to be catched or it climbs up the stack. Exceptions make it much easier to find out where an error happens (if they have proper content, they also say why it happened).

Why cant I simply check if a variable is null instead of checking for different exceptions?

2 Answers2