Pushdown Automaton Simulator

[artemis_f]

This is homework. Before this I have myself managed to create a NFA to DFA converter in Java and then something that can take a string and say if the dfa can accept string or not for some other assignment. However for PDAs I am stuck because I do not know how to deal with the non determinism.

I am trying to create my program using Java. The program is given a string and a PDA (specified in the structure written in lines in a file where each line is like the following:
currentState inputSymbolToBeConsumed SymbolAtTopOfStack ResultingState StringWhichReplacesTopOfStack

Since PDA is non deterministic a state can have more than one transition to another state and the program has to explore multiple paths simultaneously. But it should only explore a path until a set number of transitions and if it can't then that path should be abandoned.

What I need is for someone to explain to me what type of methods I am going to need:
So far I have the following methods:
In a Reader class:
getAcceptingState (reads final states into a data structure)
getStartingState (reads startiing states into a data structure)
getTransitions (which reads all transitions into an ArrayList<String[]> so I can access the various elements)

In the PDA class:
public ArrayList<String> getTransitionState(String filename, String inputSymbol, String inputState, Stack stack)
[this returns all the states a state will transition to]

public ArrayList<String> getTransitionStack(String filename, String inputSymbol, String inputState, String inputStack)
[this one notes all the StringWhichReplacesTopOfStack for each transitioned to state. The first string is seperated by the other one with a *** so basically I can extract the info I want though it is not ideal]

public Stack modifyTheStack(String filename, String alph, String stateIs, Stack stackIs){
[this takes the current stack and modifies it based on the current state. I am not sure I have the rules correct so I shall post here so someone can tell me if I am wrong]

public Stack modifyTheStack(String filename, String alph, String stateIs, Stack stackIs){
		
	String stackTopIs = stackIs.peek().toString();
	ArrayList<String> stackWillBe = getTransitionStack(filename, alph, stateIs, stackTopIs);
		
	//for s(q,a,X)->(p,y) if y=EPSILON then pop stack
	if (stackWillBe.contains("EPSILON")){
		stackIs.pop();
		System.out.println("if (stackWillBe.contains(EPSILON) popstackIs: " + stackIs);
	}
	//if y=X stack is unchanged
	String stackStrTemp = stackWillBe.get(0);
	if ((stackWillBe.size()==1)&&(stackStrTemp==stackTopIs)){
			System.out.println("if ((stackWillBe.size()==1)&&(stackStrTemp==stackTopIs)):do noth ");//do nothing
	}
		
	Stack stackIsTemp = new Stack();	
	//if y = YZ then X is replaced by Z and Y is pushed on stack
	if (stackWillBe.size()>=1){
		stackIs.pop();
		for (int sz=0; sz<stackWillBe.size(); sz++){
		//store in temp stack because elements being added in reverse order
		        stackIsTemp.add(stackWillBe.get(sz));	
		}
			
		//if X is empty then push y
		if (stackTopIs=="EPSILON"){
			for(int s=0; s<stackIsTemp.size(); s++){
			stackIs.add(stackIsTemp.pop().toString());
			}
		}
		else{
			//new stack top is meant to be Y
			for(int s=0; s<stackIsTemp.size(); s++){
			stackIs.add(stackIsTemp.pop().toString());
			}
		}
	}//end if stack is > 1
		
         return stackIs;
}

And finally I have
public ArrayList<String> epsilonTransition(String filename, String inputState, Stack stackIs)
Which returns stateThenStackSymbols so I can basically extract the info I need from it.

What I really, really, need to know now is If I have gone off in completely the wrong direction? If I have how can I get back on the right track. If I am on the right track then how can I bring this all together to actually implement the recursion this program obviously needs? Could someone explain what type of methods I need to create and what they should be doing?

I would be really really greatful for any insight you can give me. I have scoured heaps of internet sites and not found anything to help me I'm afraid.

Let me know if you actually need to see my code to help me.