java - Game Loop control -

i'm having tremendous difficulty understanding piece of code controls loop of game... can't understand purpose of while loop "while(unprocessedseconds > secondsforeachtick)" , why fps counter if inside of if(tickcounter % 60 ==0) follows on code:

public void run()  {     int frames = 0;     double unprocessedseconds = 0;     long previoustime = system.nanotime();      double secondsforeachtick = 1/60.0;        int tickcount = 0; //render counter     boolean ticked = false;      while (running)      {         long currenttime = system.nanotime();         long passedtime = currenttime - previoustime;          previoustime = currenttime;          unprocessedseconds = unprocessedseconds + passedtime / 1000000000.0;          int count = 0;         while(unprocessedseconds > secondsforeachtick)         {                tick();             count++;             unprocessedseconds -= secondsforeachtick;               ticked = true;             tickcount++;              if(tickcount % 60 == 0){                 system.out.println(frames + " fps");                 previoustime += 1000;                 frames = 0;             }         }         system.out.println("iterações loop: "+count);          if(ticked)         {             render();             frames++;             ticked = false;         }      } } 

that inner while cycle ensures game update based on fixed time, rather frame time. unprocessed time getting collected , greater time frame 1 tick, calles tick().

the tickcount counts ticks (the tick time 1/60 sec, 60 tick/sec), , 1 sec elapsed prints collected frames (so fps). also, ticked signals may changed in game, new render required.