Determine whether a method has been called the first or the second time?

Question

I want to implement a method which has a different behavior when called for the first time, and then when it is called for the second time.

How to do that?

Answer 1

Instance methods in Java have access to the state of the class. Add a variable to indicate whether or not the methods has been called before, and use it to decide between two paths to take inside the method:

class FirstTimeCaller {
    private boolean isFirstTime = true;
    void methodWithState() {
        if (isFirstTime) {
            ... // Do first-time thing
            isFirstTime = false;
        } else {
            ... // Do the other thing
        }
    }
}

This works for instance methods of the same object: first-time call will be executed the first time you call methodWithState on each new object of FirstTimeCaller class.

If you wish to implement the same behavior for a static method, or you'd like to have the first invocation on any instance to do a different thing, and all subsequent calls to do something else, make isFirstTime field static.

Answer 2

You can simply create a variable

int counter = 0; // This means the method has not been called yet

And when the method is called then just do this code in it:

counter++; // Increment by 1 for each new call

And you have a number of method calls stored in a variable "counter" so you can choose what to do with it.