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
– Sanjeev, Commented Jun 29, 2016 at 12:51
This may be useful: stackoverflow.com/q/970029/423955 Java primitive types cannot be null. Only references to Objects can be null. — Alessandro Da Rugna
– Alessandro Da Rugna, Commented Jun 29, 2016 at 12:51
Possible duplicate of Validating input using java.util.Scanner — Tom
– Tom, Commented Jun 29, 2016 at 12:55

score 4 · Accepted Answer · 2016-06-29 13:05:53Z

4

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

edited Jun 29, 2016 at 13:05

answered Jun 29, 2016 at 12:50

user6499716

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9 Comments

Andy Turner Over a year ago

Please be more precise: an int cannot be null; an Integer can; integer is not a thing in Java.

user6499716 Over a year ago

I did say integer not Integer and int is short for: integer.

Andy Turner Over a year ago

@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).

user6499716 Over a year ago

@FelixRosén Have a look at this: docs.oracle.com/javase/7/docs/api/java/lang/Integer.html

Andy Turner Over a year ago

@FelixRosén yes. Integer usually refers to java.lang.Integer; integer is not a standard type in Java.

|

JF Meier · Accepted Answer · 2016-06-29 12:52:24Z

0

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).

answered Jun 29, 2016 at 12:52

JF Meier

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