//An instance of this class represents a sequence of Positions
//Each member of the sequence is orthogonally adjacent to its
// predecessor and successor.
//A Position in this Path occurs no more than once in this Path
import java.util.ArrayList;
public class Path
{
   //Instance Variable
	private ArrayList<Position> path;
	
   //Constructor
	public Path()
	{
		this.path = new ArrayList<Position>();
	}
	
   //Accessor: 
   //Returns COPIES of the Positions in this Path in the
   // same order in which they occur in this Path
	public Position[] getPath()
	{
      return null;
	}
	
   //Mutator:
   //Add a new Position after the current last Position in this Path
   //A Runtime Exception is thrown if
   // - the new Position duplicates a Position already in this Path
   // - the new Position is not adjacent to the last Position
	public void extend(Position step)
	{
	}
	
   //Mutator:
   //Remove and return the last Position from this Path
   //A Runtime Exception is thrown if this Path is empty
	public Position backUp()
	{
      return null;
	}
	
   //Override
	public String toString()
	{
		return "";
	}
}