How to modify private static variable through setter method

Question

I have the following variable in a class named Example:

private static int number;

If I wanted to assign the variable a number using an outside class, which would I do?

1) Make the setter method in Example static so I can access it like this:

Example.setNumber(3);

2) or Make the setter method non-static so I create an object of Example to set the number

Example e = new Example()
e.setNumber(3);

What are the differences between the two and which one is the better way?

Answer 1

It is recommendable to use a static method in this case.

Why? Well, if you make it a non-static method, that would lead to the following suprising effect:

Example e1 = new Example();
Example e2 = new Example();

e2.setNumber(3);
e1.setNumber(5);

System.out.println(e2.getNumber()); // surprise! prints 5,     

So even though you called the method on e1, e2 is also affected. The corresponding static example is much less surprising:

Example e1 = new Example();
Example e2 = new Example();

Example.setNumber(5);
System.out.println(Example.getNumber()); // prints 5, no surprise...