Call a block of a method only for the first call of the method

Question

I have a method and inside this method I have a block:

public void method()
{
   [block instructions]
}

But this method is called twice in

Answer 1

At the risk of greatly over-engineering I actually suggest state-pattern. Essentially you have a State abstraction:

interface State extends Runnable {}

with two implementations:

class FirstState extends State {
    public void run() {
        //[block of code]
        state = new SecondState();
    }
}

class SecondState extends State {
    public void run() {
        //[block instructions]
    }
}

The FirstState switches current state:

private State state = new FirstState();

Your method() now has no conditional logic:

public void method()
{
    state.run();
}

However in 99% of cases boolean flag is enough...

UPDATE: the solution above is not thread-safe. If you need it, simple AtomicReference state won't will be enough (see Marko Topolnik comment below) or you need to synchronize the whole method():

public synchronized void method()
{
    state.run();
}