public class Timer {

    private long timeThen;

    private static final long measureInterval = 1000 * 1000000L; // one second
    private long lastMeasure = System.nanoTime();
    private int frameCounter;
    private long fps;

    /**
     * Creates a new Timer.
     */
    public Timer() {
        timeThen = System.nanoTime();
    }

    /**
     * Attempts to sync the timer with the specified fps.
     * @param fps the fps to sync with.
     */
    public void sync(int fps) {
        updateFPS();

        long gapTo = 1000000000L/fps + timeThen;
        long timeNow = System.nanoTime();

        try {
            while (gapTo > timeNow) {
                Thread.sleep((gapTo-timeNow) / 5000000000L);
                timeNow = System.nanoTime();
            }
        } catch (Exception e) {}

        timeThen = timeNow;
    }

    /**
     * Calculates the fps.
     */
    private void updateFPS() {
        this.frameCounter++;

        long now = System.nanoTime();
        if(now >= this.lastMeasure + measureInterval) {
           this.fps = this.frameCounter;
           this.frameCounter = 0;
           this.lastMeasure += measureInterval;
        }
    }

    /**
     * The Timer automatically tries to calculate the fps it's running on.
     * This method returns that value. It updates once every second.
     * @return the current fps this timer is running in.
     */
    public long getFps() {
        return this.fps;
    }

}