How do I translate one of my functions into an Iterable<T> function?

Question

Im working on a code to implement different search functions to solve the Farmer Wolf Goat Cabbage problem. We were given several classes that our main and FarmerWolfGoatCabbage class implemented. One of the classes, AbstractSolver includes the line

        Iterable<AState> moves = s.getPossibleMoves();
        for (AState move : moves)
            if (!closed.contains(move))
                addState(move);

Here is my FarmerWolfGoatCabbage class.I basically want to translate the following function

public DepthFirstSolver getPossibleMoves1(){

    DepthFirstSolver moves = null;

    //use getOpposite() and addIfSafe
    FarmerWolfGoatState fwgsParent = new FarmerWolfGoatState();
    FarmerWolfGoatState fwgsChild = null;
    int hash;
    // the farmer's current position before crossing the river
    Side farmerCurrent = this.farmer;

    if(this.wolf == farmerCurrent){
        fwgsChild = new FarmerWolfGoatState(this, this.getOpposite(this.farmer),
                    this.getOpposite(this.wolf), this.goat, this.cabbage);
        hash = fwgsChild.hashCode();
        if(addIfSafe(hash))
            moves.addState(fwgsChild);  
        System.out.println("W");
    }

    if(this.cabbage == farmerCurrent){
        fwgsChild = new FarmerWolfGoatState(this, this.getOpposite(this.farmer),
                    this.wolf, this.goat, this.getOpposite(this.cabbage));
        hash = fwgsChild.hashCode();
        if(addIfSafe(hash))
            moves.addState(fwgsChild);  
        System.out.println("C");
    }   

    if(this.goat == farmerCurrent){
        fwgsChild = new FarmerWolfGoatState(this, this.getOpposite(this.farmer),
                    this.wolf, this.getOpposite(this.goat), this.cabbage);
        hash = fwgsChild.hashCode();
        fwgsChild.getPosition();
        //

        if (fwgsChild == null)
            System.out.println("NULL");

        if(addIfSafe(hash))
            //moves.addState(fwgsChild);
        System.out.println("G");
    }

    return moves;
}

into a similar function but with the Iterable return type

public Iterable<AState> getPossibleMoves() 
{
}

Answer 1

Iterable is an interface:

http://download.oracle.com/javase/6/docs/api/java/lang/Iterable.html

Your FirstDepthSolver class needs to implement that interface as that is what you're returning from getPossibleMoves1(). Subsequently this means you're going to have to implement Iterator (or else store whatever it is you're needing to iterate over in a java Collection that already provides an interator, and return that).

I suspect that's what the assignment is trying to get you to do in addition to solving the problem at hand.

This SO question should be of some help: How can I implement the Iterable interface?

Answer 2

Make DepthFirstSolver a wrapper class with a member variable of type Collection. Then on the constructor of DepthFirstSolver, instantiate the member variable to some type of collection (as you want....ArrayList). Create an add method on the DepthFirstSolver class to call the member variables add class. Add an iterator method in DepthFirstSolver to call the iterator of the member variable. This way you do not need to change your FarmerWolfGoatCabbage except calling the iterator of DepthFirstSolver at the end as return value.