Lets say...
<T, S extends T> void work(final Class<T> type, final S object) {}
or
<T> void work(final Class<T> type, final T object) {}
How can I pass following parameters to work()?
final Class<?> type = <not null> // This is actually an reflection output.
final Object object = <not null>
assert type.isInstance(object); // this is absolutely guaranteed
work(type, type.cast(object)); // compile error; how can I do this?
work(type, object); // compile error; how can I do this?
You'd need a Class<T> for this to work, but you can get that. Once you have that, you can simply do this:
work(type, type.cast(object));
Now, since you've got a Class<?> you can't simply assign it to a Class<T>, but you can work around this by providing an additional method:
<T> void checkedWork(final Class<T> type, final Object object) {
work(type, type.cast(object));
}
isInstance check to checkedWork since that'd have to be done anyway.
Class.cast() will throw a ClassCastException if the types don't match at runtime, so I'd say that's even more appropriate than using an assert.cast() call. But the decision between assert/cast() is not relevant here, since both only happen at runtime.S extends T doesn't make much sense.Change final Class<?> type to final Class<Object> type (or to whatever concrete type you have). In your definition you have S extends T but if you pass in Class<?> you'd get T = ? and the compiler could not check whether Object extends ? (since ? could be anything).
Edit:
Alternatively, change work to <T, S> void work(final Class<T> type, final S object) {}.
S extends T. If this requirement is not that rigid (he's checking for isInstance anyway), then the declaration of work should just contain <T, S>.S extends T more rigid than isInstance?S extends T is not more rigid, but the requirement itself is: The object passed in must be of type T or a subclass. isInstance just moves the check for this requirement to runtime. With isInstance you could just remove the compile time check.
The compiler cannot check that the object is an instance of type. You can do this at runtime as you have done. The simplest way to get this to compile is to use
final Class type = <not null>
This will give you a warning that the type is unchecked.
void work(Class<?> type, Object object)and I put a conditional check fortype.isInstance(object). Did I do right? Thank you.