When you make an ArrayList without specifying the object type, does it create it automatically when you add the first object?

Question

For example, instead of doing

ArrayList<ClassName> variableName; 

you do

ArrayList variableName; 

then later you add an object of type "ClassName"

variableName.add(objectName); 

will that automatically set the type of your array as

ArrayList<ClassName> 

?

Answer 1

No. Generics are for compile time only. You are just losing the benefit of that check. At runtime all generic information is erased

In other words,

ArrayList<Type>  

at runtime is just an ArrayList. The benefit of doing that over just a List is that when you are writing your code, the compiler will check that you dont put anything inappropriate in your list.