[WesleySnipes]

So, I have to implement a deadlock free version of the dining philosopher problem. I am using wait() and signal() methods to ensure that two adjacent philosophers aren't picking up the same chopstick. Here is my code

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

public class DiningServerImpl implements DiningServer {
	// different philosopher states
	enum State {
		THINKING, HUNGRY, EATING
	};

	// number of philosophers (a constant)
	public static final int numOfPhils = 5;

	// array to record each philosopher's state
	State[] states = new State[numOfPhils];
	Condition[] self = new Condition[numOfPhils];

	// synchronization variables (Lock and Condition)
	Lock lock;

	public DiningServerImpl() {
		// array of philosopher's state
		// originally all philosopher's are thinking
		for (int i = 0; i < numOfPhils; i++) {
			states[i] = State.THINKING;
		}

		lock = new ReentrantLock();

		for (int i = 0; i < numOfPhils; i++)
			self[i] = lock.newCondition();
	}

	// the method called by a philosopher when they wish to eat
	public void takeForks(int philNum) {
		states[philNum] = State.HUNGRY;
		test(philNum);
		if (states[philNum] != State.EATING) {
			System.out.println(philNum + " CAN'T EAT OMG");
		      while ( states[philNum] != State.EATING) {
		          try { self[philNum].wait(); }
		          catch(InterruptedException e) {}
		       }
		}

	}

	// the method called by a philosopher when they are finished eating
	public void returnForks(int philNum) {
		states[philNum] = State.THINKING;
		test((philNum + 4) % 5);
		test((philNum + 1) % 5);
		lock.unlock();
	}

	private void test(int i) {
		if ((states[(i + 4) % 5] != State.EATING)
				&& (states[i] == State.HUNGRY)
				&& (states[(i + 1) % 5]) != State.EATING) {
			states[i] = State.EATING;
			self[i].signal();
	        
		}

	}
}

and I'm getting an error when using self[i].signal and I'm not sure why. Can anyone help? Here is a sample output.

philosopher 0 is thinking.
philosopher 3 is thinking.
philosopher 2 is thinking.
philosopher 1 is thinking.
philosopher 4 is thinking.
philosopher 2 is hungry.
philosopher 1 is hungry.
philosopher 4 is hungry.
1 CAN'T EAT OMG
Exception in thread "Thread-2" Exception in thread "Thread-4" Exception in thread "Thread-1" java.lang.IllegalMonitorStateException
	at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.signal(Unknown Source)
	at DiningServerImpl.test(DiningServerImpl.java:61)
	at DiningServerImpl.takeForks(DiningServerImpl.java:37)
	at Philosopher.run(Philosopher.java:26)
	at java.lang.Thread.run(Unknown Source)
java.lang.IllegalMonitorStateException
	at java.lang.Object.wait(Native Method)
	at java.lang.Object.wait(Object.java:503)
	at DiningServerImpl.takeForks(DiningServerImpl.java:41)
	at Philosopher.run(Philosopher.java:26)
	at java.lang.Thread.run(Unknown Source)
java.lang.IllegalMonitorStateException
	at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.signal(Unknown Source)
	at DiningServerImpl.test(DiningServerImpl.java:61)
	at DiningServerImpl.takeForks(DiningServerImpl.java:37)
	at Philosopher.run(Philosopher.java:26)
	at java.lang.Thread.run(Unknown Source)
philosopher 0 is hungry.
0 CAN'T EAT OMG
Exception in thread "Thread-0" java.lang.IllegalMonitorStateException
	at java.lang.Object.wait(Native Method)
	at java.lang.Object.wait(Object.java:503)
	at DiningServerImpl.takeForks(DiningServerImpl.java:41)
	at Philosopher.run(Philosopher.java:26)
	at java.lang.Thread.run(Unknown Source)