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Java Java Objects Harnessing the Power of Objects Incrementing and Decrementing

How to use nonstatic method inside the class without an object

He has used isEmpty() method which is non static without creating an object in if(!isEmpty) how this is possible

1 Answer

28,556 Points

He calls the isEmpty method within dispense which is itself a non-static method. That means that there is no way to run that code without first creating an instance of the class.

When Java encounters a call to a method that is found within the object it is treated as a call to that object's method. So isEmpty() is equivalent to this.isEmpty().

Referencing a non-static method or field variable within a class is only an issue if the code is written inside a static method, within non-static methods it poses no problem since an object is guaranteed to exist when the code is ran.

what do you mean by "When Java encounters a call to a method that is found within the object it is treated as a call to that object's method"

28,556 Points

I mean that when you call a method that has a name that matches a method that exists in the current object, then it will automatically call that method, even though you did not specify where the method is from.

So if you create an instance of Dispenser called dis and called dis.dispense() when Java encounters the call to isEmpty() it looks for a method called isEmpty within the object stored in dis, and if it finds one it then that is the method it runs.

And since you cannot call dispense without creating an object first this will always be what happens, which is why calling the isEmpty method works.