Java difference between List and List<Object>

Question

What is the difference between List and List<Object> in java?

Answer 1

Suppose you've got two lists:

List<Object> mainList = new ArrayList<Object>();

and one with a raw type:

List rawList = new ArrayList();

Now let's do something like this:

List<Integer> intList = new ArrayList<Integer>();
intList.add(42);
mainList.addAll(intList);
rawList.addAll(intList);

But there is somewhere one more list which contains String objects:

List<String> strList = new ArrayList<String>().

When we try to call

strList.addAll(mainList)

we get a Compilation Error :

The method addAll(Collection<? extends String>) in the type List<String> is not applicable for the arguments (List<Object>).

But if we try to call

strList.addAll(rawList)

we get just a warning.

So if you are using only lists of objects in your application it's really no difference between List and List. But since Java 1.5 it's a good idea to use generics for providing compile-time type safety for your application.