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The syntax for a generic method includes a list of type parameters, inside angle brackets, which appears before the method's return type. For static generic methods, the type parameter section must appear before the method's return type.
A generic type is defined using one or more type variables and has one or more methods that use a type variable as a placeholder for an argument or return type. For example, the type java. util. List<E> is a generic type: a list that holds elements of some type represented by the placeholder E .
In generic code, the question mark (?), called the wildcard, represents an unknown type. The wildcard can be used in a variety of situations: as the type of a parameter, field, or local variable; sometimes as a return type (though it is better programming practice to be more specific).
I noticed that if I use generics on a method signature to accomplish something similar to co-variant return types, it works like I think it would, except it generates a warning:
interface Car {
<T extends Car> T getCar();
}
class MazdaRX8 implements Car {
public MazdaRX8 getCar() { // "Unchecked overriding" warning
return this;
}
}
With the code above, my IDE gives the warning: "Unchecked overriding: return type requires unchecked conversion. Found: 'MazdaRX8', required 'T'"
It makes little sense to me, and Google didn't bring up anything useful. Why doesn't this serve as a warning-free replacement for the following interface (which is also warning free, as co-variant return types are allowed by Java)?
interface Car {
Car getCar();
}
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