Adding a delay without Thread.sleep and a while loop doing nothing

One of approaches is :

class Timer {
            private static final ScheduledExecutorService scheduledThreadPoolExecutor = Executors.newScheduledThreadPool(10);
    
            private static void doPause(int ms) {
                try {
                    scheduledThreadPoolExecutor.schedule(() -> {
                    }, ms, TimeUnit.MILLISECONDS).get();
                } catch (Exception e) {
                    throw new RuntimeException();
                }
            }
        }

and then you can use Timer.doPause(50) where you need.

Something like the following should give you the delay you need without holding up the game thread:

private final long PERIOD = 1000L; // Adjust to suit timing
private long lastTime = System.currentTimeMillis() - PERIOD;

public void onTick() {//Called every "Tick"
    long thisTime = System.currentTimeMillis();

    if ((thisTime - lastTime) >= PERIOD) {
        lastTime = thisTime;

        if(variable) { //If my variable is true
            boolean = true; //Setting my boolean to true
            /**
            *Doing a bunch of things.
            **/
            //I need a delay for about one second here.
            boolean = false; //Setting my boolean to false;
        }
    }
}

long start = new Date().getTime();
while(new Date().getTime() - start < 1000L){}

is the simplest solution I can think about.

Still, the heap might get polluted with a lot of unreferenced Date objects, which, depending on how often you get to create such a pseudo-delay, might increase the GC overhead.

At the end of the day, you have to know that this is no better solution in terms of processor usage, compared to the Thread.sleep() solution.