[hardwired]

Code:

import java.util.Random;

public class GarageTest 
{
    public static void main(String[] args)
    {
        Garage garage = new Garage();
        Entrance entrance1 = new Entrance(garage, 1);
        entrance1.start();

        Exit exit1 = new Exit(garage, 1);
        exit1.start();

        Entrance entrance2 = new Entrance(garage, 2);
        entrance2.start();

        Exit exit2 = new Exit(garage, 2);
        exit2.start();
    }
}

class Garage
{
    public static int TOTAL = 10;
    int currentNumber = 0;

    public synchronized void enter(int id, int carNumber) {
        while (currentNumber == TOTAL) {
            try {
                wait();
            } catch (InterruptedException e) { }
        }
        currentNumber++;
        System.out.printf("Car %2d entered at %d  " +
                          "currentNumber = %d%n",
                           carNumber, id, currentNumber);
        notifyAll();
    }

    public synchronized void exit(int id) {
        while (currentNumber == 0) {
            try {
                wait();
            } catch (InterruptedException e) { }
        }
        currentNumber--;
        System.out.println("Car    exited  at " + id +
                           "  currentNumber = " + currentNumber);
        notifyAll();
    }
}

class Entrance extends Thread
{
    Garage garage;
    int number;

    public Entrance(Garage garage, int threadNum)
    {
        this.garage = garage;
        number = threadNum;
    }

    public void run()
    {
        for(int j = 0; j < 10; j++)
        {
            garage.enter(number, j+1);
        }
    }
}

class Exit extends Thread
{
    Garage garage;
    int number;
    Random seed = new Random();

    public Exit(Garage garage, int threadNum)
    {
        this.garage = garage;
        number = threadNum;
    }

    public void run() {
        for (int j = 0; j < 10; j++) {
            garage.exit(number);
            try {
                sleep(2000 + seed.nextInt(3000));
            } catch (InterruptedException e) {
                break;
            }
        }
    }
}