Asking for some basic concept related to InventoryClick

So what I am going to ask is about "relationship between variable and player"
Assume that I have the code like this

Code:

public class HelloWorld{
    int page 1;
    @EventHandler
    public void onInventoryClick(InventoryClickEvent event) {
        if (#Some conditions#) page++;
    }
}

Also assume I have 2 players named "Steve" and "Alex"
When "Steve" trigger the event ONCE, variable "page" will add 1 for sure
But when "Alex" trigger the event ONCE and right after "Steve" trigger it, variable "page" will add 1 more

What I'm going to ask is:
How to code that 2 players have different variable value of "page" without setting player's metadata?
Also it will be cleared when player close inventory/server restart/player left/whatever...?
(Or I can initialize the variable for player when they open the inventory again)

Thank you.

(I'm coding a multi-page item display tbh. It's harder than I think...)

 

Oh that's right! You've reminded me
I'll give it a shot