Java - add time delay to a cycle flow

Question

I need to add time delay between cycle flow like this:

    public boolean timeDelay(int seconds) {
        // 1000000000 ns = 1 s
        if (/* some system method to start calculate time in seconds*/ == seconds) {
            return true;
        } else {
            return false;
        }
    }

    public void renderEnemies() {
        for (int w = 0; w < wave.size(); w++) {
            while(timeDelay(2)){
                (wave.get(w)).render();
            }
        }
    }

Maybe my thinking isn't good, but I need to do like this... wave --> ArrayList of enemies in my game Render enemies is in game loop after pressing button "NextWave" and I need to spawn them with delay between them like a --> 2s * 2s * 2s * 2s * 2s * where * is enemy...

Can you help me?

Answer 1

You should probably thread it and use sleep as @curiosu mentions.

However, if you don't want to use sleeps/multiple threads but do want it to be pseudo real time (not turn based) you'll need a driving loop at the top of your game like so:

boolean keepPlaying = true;
while(keepPlaying) {
  doNpcStep()
  doPlayerStep()
  keepPlaying = !isGameOver()
}

Each of these steps needs to run in a very small time slice, then in the doNpcStep function you get the current time, find the offset from a start time and run any action that should happen by now.

You could, for example, do this by keeping a min priority queue where priority is equal to the time they should execute by (in ms since start of java epoch). Then take all elements off the queue that are less than or equal to current time and run them, placing new occurrences onto the queue as necessary.

In essence this is a simulation of running a player and npc thread, where you are in charge of how much time each gets to run for.