问如何让AtomicInteger在Runnable类中工作

EN

public class GarageWorker {
    public static void main(String[] args) {
        System.out.println("We are going to count the vehicles in the garage");
        System.out.println();
        System.out.println("There are 50 vehicles in the garage to start with!");
        System.out.println();

        GarageWorker garage = new GarageWorker(50);

        Runnable vehicleEnter = garage.new Enter();
        Runnable vehicleExit = garage.new Exit();

        Thread thread1 = new Thread(vehicleEnter);
        Thread thread2 = new Thread(vehicleExit);

        thread1.start();
        thread2.start();
    }

    public GarageWorker(int initialCarCount) {
        counter = initialCarCount;
    }

    public int counter;

    public class Enter implements Runnable {
        public Enter() {

        }

        public int increaseVehicleCount() {
            return ++counter;
        }

        public void run() {
            while (counter < 100) {
                System.out.println("One vehicle entered the garage now there are " + increaseVehicleCount());
            }
        }
    }

    public class Exit implements Runnable {
        public Exit() {

        }

        public int decreaseVehicleCount() {
            return --counter;
        }

        public void run() {
            while (counter > 0) {
                System.out.println("One vehicle left the garage now there are " + decreaseVehicleCount());
            }
        }
    }
}