java - Type mismatch: cannot convert from ASuperClass to ASubClass -

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when have thes codes:

asuperclass super1 = new asuperclass();  asubclass sub1 = new asubclass(3);  sub1 = (asubclass) super1; // line compiled ok has runtime error  line 3  asubclass sub2 = new asuperclass(); // line compiled not ok  line 4

my question why error in line 3 ("asuperclass cannot cast asubclass") in line 3 runtime error not compile error similar error in line 4 , compile error. logics behind that? many thanks!

you're getting runtime error because you're telling compiler (by explicit cast) trust you're not making errors, it's ignoring errors , doesn't detect in compilation time. when program runs, you'll exception since super1 asuperclass , not asubclass.

in second case, you're getting compilation error since compiler knows making mistake (and you're not telling him trust casting example).


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