Handling of corner cases may be a bit different than in a programming language like Java.
Let's have a look at the following examples in order to understand the differences.
To make the analysis simpler, let's assume that there is only one Motorbike object stored in a Hazelcast Map.
| Id | Query | Data state | Extraction Result | Match |
|---|---|---|---|---|
| 1 | Predicates.equal('wheels[7].name', 'front-wheel') | wheels.size() == 1 | null | No |
| 2 | Predicates.equal('wheels[7].name', null) | wheels.size() == 1 | null | Yes |
| 3 | Predicates.equal('wheels[0].name', 'front-wheel') | wheels[0].name == null | null | No |
| 4 | Predicates.equal('wheels[0].name', null) | wheels[0].name == null | null | Yes |
| 5 | Predicates.equal('wheels[0].name', 'front-wheel') | wheels[0] == null | null | No |
| 6 | Predicates.equal('wheels[0].name', null) | wheels[0] == null | null | Yes |
| 7 | Predicates.equal('wheels[0].name', 'front-wheel') | wheels == null | null | No |
| 8 | Predicates.equal('wheels[0].name', null) | wheels == null | null | Yes |
As you can see, no NullPointerExceptions or IndexOutOfBoundExceptions are thrown in the extraction process, even
though parts of the expression are null.
Looking at examples 4, 6 and 8, we can also easily notice that it is impossible to distinguish which part of the
expression was null.
If we execute the following query wheels[1].name = null, it may be evaluated to true because:
-
wheelscollection/array is null. -
index == 1is out of bound. -
nameattribute of the wheels[1] object isnull.
In order to make the query unambiguous, extra conditions would have to be added, e.g.,
wheels != null AND wheels[1].name = null.