handling a null input argument in a method which returns an int

[sridhar signon]

  
public static int getClassType(EEUFdn fdn) {        
        EEURdn rdn = fdn.getLastRdn();
        return classTypeMap.get(getCMDBClass(rdn.getClsType()));
}

If fdn is null, what is the best practice
-throw an runtime exception
-check for null, and return 0

[Sebastian Janisch]

It really depends what your requirements are.

If 0 is a value that could be a valid value that comes from the computation, it is probably a bad approach.

If you resign from throwing an exception, agree on an error value and document it. If you do use Exceptions, document the exeption as being thrown when there is no value available.

[John Bengler]

Hi Sridhar,

I would say that depends. If you're able to return a value that makes sense then return it, if not throw e.g. an IllegalArgumentException..

If there is any doubt I would prefer to throw an error, according to the crash early principle, which says that in case of an error an application should crash as early as possible.


John

[Campbell Ritchie]

Agree with John Bengler, but since there already is a built-in Exception specially designed for that occurrence, best to use that class.

[sridhar signon]

I will use the IllegalArgumentException and document it in the method comments. The return value of 0 may not make sense in my case. Thanks to you all.

[David Newton]

Is the argument *likely* to be null? Or is it a programming error if it's null?

[Suren Singh]

Suppose your code snippet looks like

public void doSomeStuff(String str){

// here your are invoking some methods on other objects

otherObject.somemethod();


}

Should we check for non nullness of otherObject as well , if its null it will throw NPE.

What does the best practice says about validatin an object before invoking any methods on them .

[Campbell Ritchie]

You should have checked otherObject is not null earlier. If it is a field, it ought to be initialised in the constructor. If it is set by a set method, that set method ought to check for nullity and throw a NullPointerException if null is passed. As John Bengler says, "crash early".

[sridhar signon]

David Newton wrote:Is the argument *likely* to be null? Or is it a programming error if it's null?

It is a programming error if it's null. So thats why I intend to throw IllegalArgumentException in case of a null.

 
if (fdn==null)
  throw new IllegalArgumentException();

[Campbell Ritchie]

Correct to throw an Exception, but I still think NullPointerException would be better than IllegalArgumentException.ah

[David Newton]

Hmm... an IAE is more descriptive, though. Not sure what I'd do.

[Campbell Ritchie]

According to Joshua Bloch it is usual to use an NPE. In fact this situation fits the description of IAE and NPE.

[David Newton]

Yeah, I know what Bloch says. In situations like this, though, I'd rather just throw something w/ as much information as possible. I guess the message could be used to clarify.

For method pre-conditions like this I either use something like SpringContracts or I have an application-specific pre-condition exception anyway.

If it's a *programming* error this could be an assert, too.