Java泛型类

Question

I understand that in the fields of a class, you can make the field type the name of another class and then in the constructor initialise that field by calling a new class of that type, ie

public class Auction {
    private Bid bid;
}
public Auction {
    bid = new Bid();
}

The main reason for doing this is, as I understand it, to access the methods of that class.

My question is I've noticed in some methods that there are local variables created that have a type of a different class with a variable name. What is the purpose of assigning a local variable name with a type of another class? Is this another way of just accessing those methods directly, even if it hasn't been done in the fields or constructor?

Answer 1

You can do this assignment only if type of the right part is-a type of the left part. So, for example, you can use methods of left part' type with realization from right part' type.

Number number = new Integer(10);

See also OOP in Java and Polymorphism in Java .

Answer 2

First of all, you need to learn some basics about OOP. We use Objects to model the problems and solve them in Object Oriented Programming.

These "type of a different class with a variable name" is an instance of a class, which is called an Object . We can assign a variable name to an object in order to use that object and its behaviors.