Question

I dont understand why is that

for example:

class Test
{
   public void someMethod()
   {



   }

}

and then

Test test = new Test();

why is neccesary to write the type of the variable, so if you see that the variable assigns that custom class, i think that is some overflow writing).

ps: this is java, and i am new to it, so sorry if a quiestion is stupid, but i dont understand this moment

Answer 1

You’re declaring the type of the variable (reference), as distinct to the type of the object.

e.g. your variable type could be Test, or it could be a supertype (Object), or an interface that Test implements. Which one you choose depends on how your clients should refer to the initialised object. e.g. should they know it’s a particular type, or is it sufficent (or desirable) that they only know it will implement a given interface, or subset of features.

A better example would be:

Animal animal = new Dog();

in which your client code only knows that it’s dealing with an Animal. i.e. it can (say) call a method .eat(), but it won’t know that a Dog eats differently to a Fish.

Note that some languages (e.g. Scala) will perform type inference. That is, you don’t have to declare the variable type, but rather the compiler will determine what type it should be from your subsequent usage of the variable. The resultant code is still statically typed, but the compiler does more work for you.