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Java Java Objects (Retired) Meet Objects Creating Classes

Member Variable

Is a member variable just a variable that's defined within a class?

2 Answers

Ken Alger
STAFF
Ken Alger
Treehouse Teacher

Eric;

In a nutshell, yes.

Whew! That was a quick answer... okay, let's do a bit of a deeper dive into this. The official Java documentation on declaring Member Variables goes into it a bit more detail but, honestly, it wasn't enough for me. After a variety of sources of research here is how I kind of sum it up:

When we define a class, we can give that class member variables. These variables are members of that class. Take, for example, the following class declaration.

public class SomeClass {
int x;
int y;
}

SomeClass has two member variables, x & y. When we define an object instance of SomeClass it will still have two member variables, x & y. We can reference these members using the '.' character.

// Create an instance of SomeClass
SomeClass obj = new SomeClass();
// Assign new values to x & y
obj.x = 1;
obj.y = 42;

These variables belong to `SomeClass`, and are known as member variables. On the other hand, if we declare variables inside of a function, we call these local variables. These variables are local to a particular function, and not publicly accessible. For example, in the following function, we have no way of accessing the obj variable outside of the main(String[]) function.

```java
public static void main (String args[])
{
        SomeClass obj = new SomeClass();

        System.out.println ("X" + obj.x);
}

So, in the nutshell, a member variable is a variable that belongs to an object, whereas a local variable belongs to the current scope.

Hopefully that makes some sense. Please post back if you are still stuck on this concept. It is an important one as you progress through OOP languages.

Happy coding,

Ken

"So, in the nutshell, a member variable is a variable that belongs to an object, whereas a local variable belongs to the current scope."

That line right there is perfect. Thanks :)

Jason S
Jason S
16,247 Points

shouldn't myClass() be SomeClass()?