Run Loop

// Run Method
    boolean isRunning = false;
    // Variables for the FPS and UPS counter
    private int ticks = 0;
    private int frames = 0;
    private int FPS = 0;
    private int UPS = 0;
    public double delta = 0;
    // Used in the "run" method to limit the frame rate to the UPS
    private boolean limitFrameRate = true;
    private boolean shouldRender;

    public synchronized void run() {
        long lastTime = System.nanoTime();
        double nsPerTick = 1000000000D / 60D;

        long lastTimer = System.currentTimeMillis();
        delta = 0D;

        while (isRunning) {
            long now = System.nanoTime();
            delta += (now - lastTime) / nsPerTick;
            lastTime = now;

            // If you want to limit frame rate, shouldRender = false
            shouldRender = false;

            // If the time between ticks = 1, then various things (shouldRender = true, keeps FPS locked at UPS)
            while (delta >= 1) {
                ticks++;
                tick();
                delta -= 1;
                shouldRender = true;
            }

            if (!limitFrameRate && ticks > 0)
                shouldRender = true;

            // If you should render, render!
            if (shouldRender) {
                frames++;
                render();
            }

            // Reset stuff every second for the new "FPS" and "UPS"
            if (System.currentTimeMillis() - lastTimer >= 1000) {
                lastTimer += 1000;
                FPS = frames;
                UPS = ticks;
                frames = 0;
                ticks = 0;
            }
        }
        stop();
    }