Question

Possible Duplicate:
Determining the Type for a generic method parameter at runtime
Generics in static methods

The code below fails at runtime with cannot select from a type variable. Is there any way of doing this without having to pass the type as a parameter (Class<E[]> type)?

public static <E extends Deal> E[] parseDealsFromJSON(String body) {
    parser.fromJson(body, E[].class); // fails here
}

public static void main(String[] args) {
    SubDeal[] deals = parseDealsFromJSON("");
}

Answer 1

A problem is that the right hand size of = has no idea what type you want on the left hand side. i.e. java doesn’t do this kind of type inference.

A method doesn’t know what type you need a return type to be. (I have seen exceptions at runtime with MethodHandles and I suspect that Java 8 or 9 might introduce these features)

e.g. very basic type inference for return types isn’t done at runtime (or compile time)

public Double getValue() {
    return 5.0;
}

double d = m.getValue(); // not smart enough to avoid creating a `Double` here.

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With Generics you have the added bonus of type erasure. This mean E[] is actually Deal[] at runtime. Which Deal type you might have liked is lost.