Reputation: 1696

The use of static in java

I want to know if it is possible to use a static variable inside a non static methode ?

also

can I use a non static variable inside a static methode ?

Thanks

Upvotes: 0

Answers (5)

richzilla

Reputation: 42062

A static variable can be accessed from anywhere you like. A non static variable can only be accessed from a non static method or from a specific object (instance of a class).

The reason for this can get quite complicated, but in brief:

Anything that is non static in your class is duplicated whenever an object is instantiated from that class. Anything static is common to all instances of the class (and not duplicated for new objects), meaning it is unaffected by changes in the state of individual objects.

Now obviously until an instance of the class has been created, anything non static cant exist - there's no object for them to belong to. Since static members dont require an instance of a class to exist, it wouldnt be safe for them to access members that do require an instance of an object (non static).

Upvotes: 4

user85421

Reputation: 29710

Both are possible, but to access an instance (non-static) variable you need an instance.
This can be given implicitly in a non-static context like in an instance method, and must be provided explicitly in a static context.

class StaticOrNot {

    static int staticVar = 1;
    int instVar = 2;

    static void staticMethod() {
        staticVar += 1;
        StaticOrNot someInstance = new StaticOrNot();
        someInstance.instVar += 2;
    }

    void nonStatic() {
        staticVar += 1;
        instVar += 2;  // using this as instance
    }
}

Upvotes: 3

Amir Afghani

Reputation: 38561

Think about what it means to use a non-static variable in a static context. A static method is not executing on any instance - therefore, what would it mean to operate on a member field defined on the class? What instance does that field belong to? None!

The opposite scenario, namely, using a static variable in a non-static context makes perfect sense. You're on an instance, and you want to read some static reference that is defined for all instances of a given class.

Upvotes: 1