@Override
    public void update() {
        long curTime = getTime();
        lastTPF = (curTime - oldTime) * (1.0f / LWJGL_TIMER_RES);
        lastFPS = 1.0f / lastTPF;
        oldTime = curTime;
    }
<code>update</code> recalculates the frame rate based on the previous
call to update. It is assumed that update is called each frame.
jme3-lwjgl/src/main/java/com/jme3/system/lwjgl/LwjglTimer.java