Synchronization and threads problem

Question

Hi, i'm a novice to java.i got an assignement where i'm suppose to emulate a bus actions(picking on and dropping of people).
It has 4 main class , i'm using netbean as IDE.
The bus have 5 station(1,2,3,4,5) and goes to them one after another picking up passenger ad dropping them off.It have max capacity of 2 passenger at a time.It's able to pick the first passenger and leave when it reaches the 2nd station and pick the second passenger it hang as if in an infinite loop.
Here are the classes in use and screenshot depicting the sittuation:
Bus :
* Bus.java
* This class represents the bus,
* a resource shared by passengers and the control system.
package busservice;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
class Bus
public enum Direction{UP, DOWN};
private int position; // bus's currrent position, i.e. bus stop.
private int increment; // bus's currrent increment +1 for UP, -1 for DOWN
private Direction busDirection;// bus's current direction - UP or DOWN
private int available; // available seats
private ReentrantLock bus = new ReentrantLock();
private Condition[] arrive = new Condition[Main.BUS_STOPS+1]; // index 0 unused
public Bus()
available = Main.CAPACITY;
position = 1;
increment = 1; // Initially travelling in UP direction
busDirection = Direction.UP;
System.out.println(Main.spaces(position) + labelledBus()+ " arrives");
for (int i = 1; i <= Main.BUS_STOPS; i++)
arrive[i] = bus.newCondition();
// method called by a passenger wishing to get on the bus at bus stop
public void getOn(int fromStop)
bus.lock(); //passenger obtains resource
try{
while (position != fromStop || available == 0)
arrive[fromStop].await();
arrive[fromStop].signal();
available--;
catch(Exception e)
e.printStackTrace();
finally{
bus.unlock();
bus.notifyAll();
// Method called by passengers wishing to get off the bus at bus stop.
public void getOff(int toStop)
bus.lock();
try
while (position != toStop)
arrive[toStop].await();
available++; // passenger gets off train
catch (InterruptedException e)
e.printStackTrace();
finally
bus.unlock();
// returns a string showing the direction and occupancy status of the bus
private String labelledBus()
String emptySeats = "...................".substring(0, available);
String fullSeats = "*******************".substring(0, Main.CAPACITY - available);
if (busDirection == Direction.DOWN)
return ("<BUS["+emptySeats+fullSeats+"]");
else
return ("["+fullSeats+emptySeats+"]BUS>");
// Method called by control system to move bus to next bus stop
public void move()
bus.lock();
try // bus leaves one bus stop and travels to next one
System.out.println(Main.spaces(position) + labelledBus()+" leaves");
Thread.sleep(Main.TRAVEL_TIME * 1000);
position = position + increment;
System.out.println(Main.spaces(position) + labelledBus()+ " arrives");
// Reverse direction if at end of route
if ((busDirection == Direction.UP) && position == Main.BUS_STOPS)
increment = - increment;
busDirection = Direction.DOWN;
else if ((busDirection == Direction.DOWN) && position == 1)
increment = - increment;
busDirection = Direction.UP;
arrive[position].signalAll();
catch (InterruptedException e)
e.printStackTrace();
finally{
bus.unlock();
}Controler class
* Control.java
* This class implements the bus control system.
package busservice;
class Control extends Thread
private Bus bus;
private volatile boolean end = false;
public Control(Bus bus)
this.bus = bus;
public void run()
while (!end)
try
sleep(Main.WAIT_TIME * 1000);
bus.move();
catch (InterruptedException ex)
ex.printStackTrace();
return;
public void finish()
end = true;
}Passenger
* Passenger.java
* Implements a bus passenger as an autonomous thread.
package busservice;
import java.util.concurrent.CountDownLatch;
class Passenger extends Thread
private int id; // unique id, from 1 to Main.PASSENGERS
private int from, to; // start and end bus stops
private Bus bus;
private CountDownLatch CountDown;
Passenger(int id, int from, int to, Bus bus, CountDownLatch CountDown)
this.id = id;
this.from = from;
this.to = to;
this.bus = bus;
this.CountDown = CountDown;
public void run()
CountDown.countDown();
System.out.println(Main.spaces(from) + 'P' + id + " arrives");
bus.getOn(from);
System.out.println(Main.spaces(from) + 'P' + id + " gets on");
bus.getOff(to);
System.out.println(Main.spaces(to) + 'P' + id + " gets off");
this.notify();

Answer 1

* Bus.java
* This class represents the bus,
* a resource shared by passengers and the control system.
package busservice;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
class Bus
public enum Direction{UP, DOWN};
private int position; // bus's currrent position, i.e. bus stop.
private int increment; // bus's currrent increment +1 for UP, -1 for DOWN
private Direction busDirection;// bus's current direction - UP or DOWN
private int available; // available seats
private ReentrantLock bus = new ReentrantLock();
private Condition[] arrive = new Condition[Main.BUS_STOPS+1]; // index 0 unused
public Bus()
available = Main.CAPACITY;
position = 1;
increment = 1; // Initially travelling in UP direction
busDirection = Direction.UP;
System.out.println(Main.spaces(position) + labelledBus()+ " arrives");
for (int i = 1; i <= Main.BUS_STOPS; i++)
arrive[i] = bus.newCondition();
// method called by a passenger wishing to get on the bus at bus stop
public void getOn(int fromStop)
bus.lock(); //passenger obtains resource
try{
while (position != fromStop || available == 0)
arrive[fromStop].await();
arrive[fromStop].signal();
available--;
catch(Exception e)
e.printStackTrace();
finally{
bus.unlock();
bus.notifyAll();
// Method called by passengers wishing to get off the bus at bus stop.
public void getOff(int toStop)
bus.lock();
try
while (position != toStop)
arrive[toStop].await();
available++; // passenger gets off train
catch (InterruptedException e)
e.printStackTrace();
finally
bus.unlock();
// returns a string showing the direction and occupancy status of the bus
private String labelledBus()
String emptySeats = "...................".substring(0, available);
String fullSeats = "*******************".substring(0, Main.CAPACITY - available);
if (busDirection == Direction.DOWN)
return ("<BUS["+emptySeats+fullSeats+"]");
else
return ("["+fullSeats+emptySeats+"]BUS>");
// Method called by control system to move bus to next bus stop
public void move()
bus.lock();
try // bus leaves one bus stop and travels to next one
System.out.println(Main.spaces(position) + labelledBus()+" leaves");
Thread.sleep(Main.TRAVEL_TIME * 1000);
position = position + increment;
System.out.println(Main.spaces(position) + labelledBus()+ " arrives");
// Reverse direction if at end of route
if ((busDirection == Direction.UP) && position == Main.BUS_STOPS)
increment = - increment;
busDirection = Direction.DOWN;
else if ((busDirection == Direction.DOWN) && position == 1)
increment = - increment;
busDirection = Direction.UP;
arrive[position].signalAll();
catch (InterruptedException e)
e.printStackTrace();
finally{
bus.unlock();
}Controler class
* Control.java
* This class implements the bus control system.
package busservice;
class Control extends Thread
private Bus bus;
private volatile boolean end = false;
public Control(Bus bus)
this.bus = bus;
public void run()
while (!end)
try
sleep(Main.WAIT_TIME * 1000);
bus.move();
catch (InterruptedException ex)
ex.printStackTrace();
return;
public void finish()
end = true;
}Passenger
* Passenger.java
* Implements a bus passenger as an autonomous thread.
package busservice;
import java.util.concurrent.CountDownLatch;
class Passenger extends Thread
private int id; // unique id, from 1 to Main.PASSENGERS
private int from, to; // start and end bus stops
private Bus bus;
private CountDownLatch CountDown;
Passenger(int id, int from, int to, Bus bus, CountDownLatch CountDown)
this.id = id;
this.from = from;
this.to = to;
this.bus = bus;
this.CountDown = CountDown;
public void run()
CountDown.countDown();
System.out.println(Main.spaces(from) + 'P' + id + " arrives");
bus.getOn(from);
System.out.println(Main.spaces(from) + 'P' + id + " gets on");
bus.getOff(to);
System.out.println(Main.spaces(to) + 'P' + id + " gets off");
this.notify();
}