这是哪种Java成员变量？

Question

I am trying to find out what kind of member variable this is:

public class Stone {

    private Size size; // "Size" refers to a class.

I don't know what exactly this member variable is. I haven't seen a member variable as a class before. It seems to use another class as a member variable, is this correct?

Answer 1

It is an instance variable of type Size . It's perfectly fine and extremely common.

From the Java tutorial Understanding Class Members :

When a number of objects are created from the same class blueprint, they each have their own distinct copies of instance variables. In the case of the Bicycle class, the instance variables are cadence, gear, and speed. Each Bicycle object has its own values for these variables, stored in different memory locations.