Java Design Issue: Enforce method call sequence

Question

There is a question which was recently asked to me in an interview.

Problem: There is a class meant to profile the execution time of the code. The class

Answer 1

With minor changes to the interface, you can make the method sequence the only one that can be called - even at compile time!

public class Stopwatch {
    public static RunningStopwatch createRunning() {
        return new RunningStopwatch();
    }
}

public class RunningStopwatch {
    private final long startTime;

    RunningStopwatch() {
        startTime = System.nanoTime();
    }

    public FinishedStopwatch stop() {
        return new FinishedStopwatch(startTime);
    }
}

public class FinishedStopwatch {
    private final long elapsedTime;

    FinishedStopwatch(long startTime) {
        elapsedTime = System.nanoTime() - startTime;
    }

    public long getElapsedNanos() {
        return elapsedTime;
    }
}

The usage is straightforward - every method returns a different class which only has the currently applicable methods. Basically, the state of the stopwatch is encapsuled in the type system.

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In comments, it was pointed out that even with the above design, you can call stop() twice. While I consider that to be added value, it is theoretically possible to screw oneself over. Then, the only way I can think of would be something like this:

class Stopwatch {
    public static Stopwatch createRunning() {
        return new Stopwatch();
    }

    private final long startTime;

    private Stopwatch() {
        startTime = System.nanoTime();
    }

    public long getElapsedNanos() {
        return System.nanoTime() - startTime;
    }
}

That differs from the assignment by omitting the stop() method, but that's potentially good design, too. All would then depend on the precise requirements...