Answer to Question #242866 in Java | JSP | JSF for kavin

Question

The Airplane always needs to check with the Airport to see if it has an

available runway before it's able to take off or land. Simulate the above-

mentioned scenario using multi-threading.

Answer 1

public class Airport{
    static Runway r1[] = new Runway[20];
    static Plane p1[] = new Plane[30];


    public static void main(String[] args) {
        for (int i = 0; i < p1.length; i++){
            p1[i] = new Plane(i);
        }
        List<Plane> pls = Arrays.asList(p1);
        Iterator<Plane> it;
        Collections.shuffle(pls);
        it= pls.it();
        for (int i = 0; i < r.length; i++) {
            Plane p1;
            try {
                p1= it.next();
            }catch ( RuntimeException e){
                p1= null;
            }
            r1[i] = new Runway(i,p1);
        }


        for (int i = 0; i < p1.length; i++){
            Runway rw=getUsedRunway(p1[i]);
            System.out.println("plane "+p1[i].id + " is "+(rw==null?"waiting to land":("on runway "+r.id)));
        }


        for (int i = 0; i < p1.length; i++){
            p1[i].start();
        }
    }




    private static class Runway {
        private int id;
        private AtomicRef<Plane> pAtomicRef;


        public Runway(int i, Plane p) {
            id =i;
            pAtomicRef = new AtomicRef<>();
            pAtomicRef.set(p);
        }
    }




    private static class Plane extends Thread {
        private int id;


        Plane(int i){
            id=i;
        }


        @Override
        public void run() {
            Runway rw=getUsedRunway(this);
            if(rw==null){
                System.out.println("plane "+id+" wants to land");
                Runway availableRunway = availableRunway();
                while ((availableRunway=atomicallyAttempToLandPlane(this))==null) {
                    System.out.println("no runway available yet for plane " + id);
                    try {
                        sleep(30);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                System.out.println("landed plane "+id+" on runway "+availableRunway.id);
            }else {
                System.out.println("plane "+id+" wants to take off from runway "+rw.id);
                rw.pAtomicRef.set(null);
                System.out.println("plane "+id+" has taken off from runway ");
            }
        }


        
        private Runway atomicallyAttempToLandPlane(Plane plane) {
            for (int i = 0; i < r.length; i++) {
                if(r[i].pAtomicRef.compareAndSet(null,plane)){
                    return r[i];
                }
            }
            return null;
        }
    }


   
    private static Runway available_runway(){
        for (int i = 0; i < r.length; i++) {
            if(r[i].pAtomicRef.get() ==null){
                return r[i];
            }
        }
        return null;
    }


    private static Runway getUsedRunway(Plane plane){
        for (int i = 0; i < r.length; i++) {
            final Plane planeOnRunway  = r[i].pAtomicRef.get();
            if(planeOnRunway !=null && planeOnRunway.id==plane.id){
                return r[i];
            }
        }
        return null;
    }