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Generic Arrays & SCJP

 
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Hello everybody:

Does objective 6.4 of the exam cover generic arrays? I am always confused as to how detailed the exam questions will be.

I am using the Bates/Sierra study guide, and they don't cover some of the nuances of generics as in depth as the Sun Java tutorial: Generics Tutorial

Here are some code snippets:







As a note: I believe the third example is wrong. When I try this code out myself, I get a compiler error, not a compiler warning.
 
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Straight from AngelikaLanger's Generics FAQ's:


Can I create an array whose component type is a wildcard parameterized type?
No, because it is not type-safe.
The rationale is the same as for concrete parameterized types: a wildcard parameterized type,
unless it is an unbounded wildcard parameterized type, is a non-reifiable type and arrays of
non-reifiable types are not type-safe.
The array store check cannot be performed reliably because a wildcard parameterized type
that is not an unbounded wildcard parameterized type has a non-exact runtime type.
Example (of the consequences):
Object[] numPairArr = new Pair<? extends Number,? extends
Number>[10]; // illegal
numPairArr[0] = new Pair<Long,Long>(0L,0L); // fine
numPairArr[0] = new Pair<String,String>("",""); // should fail,
but would succeed
The array store check would have to check whether the pair added to the array is of type
Pair<? extends Number,? extends Number> or of a subtype thereof. Obviously, a
Pair<String,String> is not of a matching type and should be rejected with an
ArrayStoreException. But the array store check does not detect any type mismatch,
because the JVM can only check the array's runtime component type, which is Pair[] after
type erasure, against the element's runtime type, which is Pair after type erasure.



You should read this:

www.AngelikaLanger.com/GenericsFAQ/JavaGenericsFAQ.html

Thanks,
 
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