How do i solve this non-static and static variables accessing through methods for once and for all?

Question

I have always had problems with accessing private varibles in a class through a method to another class, for instance now i have this problem :

i have this variable in say class Hello1 :

    private Item[][] bankTabs;

and i want to access it through another class say hello2, so i made a public method in Hello1 that is this :

    public int amountOfItemInBank(int id) {
    int amountInBank = 0;

    for(int i = 0; i < bankTabs.length; i++) {
        for(int i2 = 0; i2 < bankTabs[i].length; i2++) {
                if (bankTabs[i][i2].getId() == id)
                    amountInBank = bankTabs[i][i2].getAmount();
        }
    }
         return amountInBank;

}

but when i want to access it through Hello2, it tells me the method is not static, and when i make it static, the variable bankTabs in amountOfItemInBank do not work and i get a lot of errors.

so when i go to Hello2 class, and i try to call this method like this :

 Hello1.amountOfItemInBank(50);

how can i solve this?

Answer 1

Either make an object of Hello1 class and then access the method

Hello1 obj = new Hello1();
int returnValue = obj.amountOfItemInBank(50);

or declare both the variable bankTabs and method amountOfItemInBank as static in Hello1 class and use Hello1.amountOfItemInBank(50); as you did earlier.

Also, read more here Understanding Class Members to clear your understanding and then you can solve the problem for once and for all.

Answer 2

Static METHODS can be called on class, and not object, like

Hello1.amountOfItemInBank(50);

To call a non-static method, you need an object of a class:

Hello1 hello = new Hello1();
hello.amountOfItemInBank(50);

The method doesn't have to be static to make use of a static field in such way. Declaring a field as static lets you use its value (if it's public) without making object of a class:

Item[][] items = Hello1.bankTabs;

or by a method call (if it's private):

Hello1 hello = new Hello1();
Item[][] items = hello.getBankTabs();


// in your class
private static Item[][] bankTabs;
public Item[][] getBankTabs() {
    return bankTabs;
}

If you do not need to access the field without instantiating the class, you probably do not want to make that variable static.