Can I use vectors to store multiple types of objects

[Nathand]

Can I use vectors to store multiple types of objects? Say I have two classes, cat & dog. Could someone show me an example of how to create a vector, and then add instances of each object type to the vector?


Thanks so much,

Nathand

[Java Tip]

Yes you can. Just call add method for different kinds of objects. While getting the object from the vector, you can use instanceof operator to test the type of the object and cast accordingly:

Vector v = new Vector();
v.add(new Cat());
v.add(new Dog());

if (v.elementAt(0) instanceof Cat) {

  Cat cat = (Cat)v.elementAt(0);

}

[danielstoner]

I have the feeling that he might mean array not Vector. But the answer is the same: create an array of Object (Object[]) and add whatever you want to it. When you need them from the array check with instanceof.

[Nathand]

Thanks so much!! That's exactly the kind of example I needed. I did mean vector instead of array, I want to use a vector because it grows sort of dynamically where with an array I have to copy things a bunch of times.

Thanks again!

Nathand

[danielstoner]

Hi Nathand,

Sorry for making assumptions about what you wanted but I am used to be kind of precise in what I say. I would've say java.util.Vector or at least Vector ;-)
One more comment - usually checking for instanceof is not a sign of a good design. In OOP you have the mechanisms to write generic code that doesn't need to check. It is way better to find a solution that is object oriented and polymorphic. For example in the above example you should strive to make everything you put in the Vector or array derived from a certain class or implementing a certain interface and define the Vector or the array as being of that type using generics. Then when you process the Vector each instance will know what to do on its own. But I am sure you know the theory ;-)

[Zosden]

You should use Generics when doing this. This way you remove a lot of run time errors to complier errors.

What you should do is.

   Vector<Object Type> myVector = new Vector<ObjectType>();

[Zosden]

instance of is a very powerful tool to use. That is why its there. Generics helps get rid of unneeded use of it though