False positive of "Dead instanceof" hint

[markiewb]

ACTUAL:

java.util.Set a = null; if (a instanceof java.util.HashSet) {} // ERROR
java.util.Set e = null; if (e instanceof java.util.ArrayList) {} //ERROR

EXPECTED:

java.util.Set a = null; if (a instanceof java.util.HashSet) {} // *NO* ERROR
java.util.Set e = null; if (e instanceof java.util.ArrayList) {} //ERROR

[FrantaM]

Why is (e instanceof java.util.ArrayList) an error? While ArrayList itself cannot be cast to Set, you can have a subclass of ArrayList that can. See http://ideone.com/sqQbM0.

[markiewb]

The hint only checks the compile-type of "e". "e" is an Set, so internally
it checks for (java.util.Set instanceof java.util.ArrayList), which returns
false.

With kind regards, markiewb

2015-04-16 11:52 GMT+02:00 FrantaM [email protected]:

Why is (e instanceof java.util.ArrayList) an error? While ArrayList
itself cannot be cast to Set, you can have a subclass of ArrayList that
can. See http://ideone.com/sqQbM0.

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[FrantaM]

I can see what it does I'm asking as to why. Instance of ArrayList can be an instanceof Set at the same time so this is still a false positive.

[markiewb]

My usecase is to catch the following construct

            java.util.Set set = xxx;
            if (set instanceof java.util.ArrayList) {
                java.util.ArrayList list = set; //<- compile error
            }

With kind regards, markiewb

2015-04-16 12:39 GMT+02:00 FrantaM [email protected]:

I can see what it does I'm asking as to why. Instance of ArrayList
can be an instanceof Set at the same time so this is still a false
positive.

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[btbouwens]

Indeed this bug is still active: I see this for f instanceof Inter for an interface Inter which isn't implemented by the type of f itself, but by possible subclasses.

[jrb0001]

Still not fixed in v1.6.0.3-SNAPSHOT:

InterfaceA something = new ClassBExtendsCImplementsA();
System.out.println(something instanceof ClassC); // Runtime: true, Netbeans: "Dead instanceof. InterfaceA cannot be assigned to ClassC"

[markiewb]

@btbouwens, @jrb0001 , @FrantaM : You are all correct. That hint makes no sense. I will remove it via #70

NB already warns you about invalid combinations.

// For example
if (new Double(42) instanceof java.util.Map) {}