OS - Criminal Transport Problem

import java.util.HashSet;
import java.util.concurrent.Semaphore;



public class CriminalTransport extends Thread{

    static Semaphore pEnter = null;
    static Semaphore cEnter = null;
    static Semaphore lock = null;
    static int police=0;
    static int criminal=0;
    static Semaphore canDrive = null;
    static Semaphore canExit = null;

    public static void init() {
        pEnter = new Semaphore(2);
        cEnter = new Semaphore(0);
        lock = new Semaphore(1);
        canExit = new Semaphore(0);
        canDrive = new Semaphore(0);
    }


static class Policeman extends Thread{

    int threadID;

    public Policeman(int threadID) {
        this.threadID=threadID;
    }

    public void execute() throws InterruptedException {
    // waits until it is valid to enter the car
    pEnter.acquire();
    System.out.println("Policeman enters in the car");
    lock.acquire();
    police++;
    if(police == 2) {
        if(criminal == 0) {
            cEnter.release(2);
        }
    }
    if(police == 3 && criminal == 0) {
        cEnter.release();
    }

    if((police+criminal == 4 ) || (police==4 && criminal==0)) {
        canDrive.release(4);
        System.out.println("Start driving.");
    }
    lock.release();
    canDrive.acquire();
    Thread.sleep(10);
    lock.acquire();
    if(police+criminal == 4) {
        System.out.println("Arrived.");
        canExit.release(4);
    }
    lock.release();
    canExit.acquire();
    System.out.println("Policeman exits from the car");
    lock.acquire();
    police--;
    if(police == 0 && criminal == 0) {
        pEnter.release(2);
        System.out.println("RELEASED 2 POLICEMAN");
    }
    lock.release();
    // when the four passengers are inside, one policeman prints the starting command

    // one policeman prints the this command to notice that everyone can exit

    // the exit from the car is allowed after the "Arrived." message is printed



  }

  public void run(){
      try {
          execute();

      }catch(InterruptedException e) {
          e.printStackTrace();
      }
  }

}

static class Criminal extends Thread{

    int threadID;

    public Criminal(int threadID) {
        this.threadID=threadID;
    }

  public void execute() throws InterruptedException {
    // waits until it is valid to enter the car
    cEnter.acquire();
    System.out.println("Criminal enters in the car");
    lock.acquire();
    criminal++;
    lock.release();
    canDrive.acquire();
    Thread.sleep(10);
    canExit.acquire();
    // the exit from the car is allowed after the "Arrived." message is printed
    System.out.println("Criminal exits from the car");
    lock.acquire();
    criminal--;
    lock.release();
  }

  public void run() {

      try {
          execute();

      }catch(InterruptedException e) {
          e.printStackTrace();
      }
  }
}



  public static void main(String[] args) throws InterruptedException {
    HashSet<Thread> threads = new HashSet<Thread>();
    for (int i = 0; i < 16; i++) {
      Policeman red = new Policeman(i);
      threads.add(red);
      Criminal green = new Criminal(i);
      threads.add(green);
    }
    // run all threads in background
    init();
    for(Thread p : threads) {
        p.start();
    }
    // after all of them are started, wait each of them to finish for maximum 1_000 ms
    for(Thread p : threads) {
        p.join(1000);
    }
    // for each thread, terminate it if it is not finished

    for(Thread p : threads) {
        if(p.isAlive()) {
            p.interrupt();
            System.out.println("Possible Deadlock!");
        }
    }

  }

}