Java Ternary Operator

[Jehan Jaleel]

Hi,

I have been coding in Java for years but never used the Java Ternary Operator that much (always did it the hard way). Now I am playing with it but the following code is not working as I expect it to...

private AdviceHeader checkIfAdviceHeaderExistsfor(
      long entityAdviceGroupDefinitionId) {
   return  adviceHeaderMap.get(entityAdviceGroupDefinitionId) != null
      ?  (AdviceHeader) adviceHeaderMap.get(entityAdviceGroupDefinitionId)
      : null;
}

Right now it is throwing an Null Pointer Exception. But I am wondering why, I just want it to return the value from the Map if it finds it or return null if it doesn't.

Thanks in advance for any help.

[Campbell Ritchie]

You need to know a lot more details.
Are you sure the Exception is actually thrown inside that method?
What sort of structure is the map: does it behave like HashMap or like Hashtable with respect to nulls?
Which reference is null? Is it the map, or the argument to that method? If the argument is a long, it is hardly likely to be null. Does the map take Longs as its Ks?

[Mike Simmons]

If line 4 is the line throwing the exception, I think the only thing that could cause the problem is if adviceHeaderMap itself is null. How is this field initialized?

[Jehan Jaleel]

Mike,

You are right, the problem is that the HashMap itself was null. I was thinking that I was not using the Ternary operator correctly and trying to cast a null.

Thanks again for your help.

[Rob Spoor]

One piece of advice: don't call methods twice if you can instead use a variable to store the results. Let's say your map was a TreeMap with millions of records. The get could take a bit of time. By calling it twice your method takes twice as long as needed.

So:

//return  adviceHeaderMap.get(entityAdviceGroupDefinitionId) != null ?
//     (AdviceHeader) adviceHeaderMap.get(entityAdviceGroupDefinitionId) : null;  
AdviceHeader header = adviceHeaderMap.get(entityAdviceGroupDefinitionId);
return header != null ? header : null;

And in this case you will immediately see that the ternary operator isn't needed; if header != null you will return header, and otherwise (header == null) you still return the value of header.

[Winston Gutkowski]

Rob Spoor wrote:One piece of advice: ...

@Jehan: Another piece of advice: DontWriteLongLines.

I've broken yours up this time; but the only reason I needed to is that your method names - while certainly descriptive - are a case of "descriptive overkill".

Maybe you had no choice in this case, but I'd definitely advise a bit of moderation if you're writing methods in the future.

Winston

[Mike Simmons]

Yeah, but now my earlier comment about "line 4" should be modified to be "lines 3-5".