generic parameters

[TopNFalvors]

Hi,

I have a generic method that can take an "integer" or "double" arrayList as a parameter and returns a value of type "double".

It works when I pass a "double" arrayList, but keeps warning about "loss of precision" when I pass an integer arrayList.

Is there anyway around this?

Thanks!

[JosAH]

Hi,

I have a generic method that can take an "integer" or "double" arrayList as a parameter and returns a value of type "double".

It works when I pass a "double" arrayList, but keeps warning about "loss of precision" when I pass an integer arrayList.

Is there anyway around this?

Thanks!

You implicitly cast something from type double to type int; as in:

double d= 3.5;
int i= d; // <--- compiler complains here

You have to make those casts explicit to show the compiler that you know what you're doing and to make it keep its mouth shut.

kind regards,

Jos

[TopNFalvors]

But what if I have something like this in the generic method:

for (int i : myArrayList)

Where "myArrayList" could by of type integer or of type double.

How do I let the generic method know whether to use int i or double i?

Thanks!

[JosAH]

But what if I have something like this in the generic method:

for (int i : myArrayList)

Where "myArrayList" could by of type integer or of type double.

How do I let the generic method know whether to use int i or double i?

Thanks!

In your for-loop you simply assume that your list contains Integers (there's also autoboxing doing some work here) which might not be true, i.e. the list might contain Doubles. So have to anticipate for that:

for (double d : myArrayList) { // possibly a widening cast to double
   int i= (int)d; // explicitly cast to int here
   ...
}

All in all I think your design is a bit shakey at best.

kind regards,

Jos

[TopNFalvors]

Thanks,

so how would you pass an arrayList into a generic class? Or is that just a bad idea?

Thanks!

[JosAH]

Thanks,

so how would you pass an arrayList into a generic class? Or is that just a bad idea?

Thanks!

Generics generally aren't a bad idea; they just can't handle primitive data types very well. If you design a class (or interface) around a type T (not primitive) your class can also handle types C<T> where C is any type that can handle a type T. Think of List<T> or even ArrayList<T> or whatever.

Your example deals with autoboxing as well (without you possibly knowing it) which makes thing even more complex because primitives (such as ints or doubles) cannot be handles by generics.

kind regards,

Jos