• If you havent already, create a RandomWalk class. Think about the attributes this class will have:
  • size of the grid,
  • a random number generator,
  • a boolean flag named done,
  • an ArrayList of points to represent the path of the random walk,
  • the start point of the walk,
  • the end point of the walk,
  • the current point of the walk,
  • as well as other instance variables as you may see fit.
• Your class must implement the RandomWalkInterface.To implement the interface, you must modify your class header as follows

  public class RandomWalk implements RandomWalkInterface{}

• Use the Point class provided in the Java standard library (in the java.awt package) to represent each point on the path. For example, the start point can be represented as:

              Point start = new Point(0,gridSize-1);            

  You can access the coordinates of the point using:

              start.x            start.y            

• Use an ArrayList of Point objects to store the path. The ArrayList class is part of the java.util package and provides functionality for managing a list of objects. There are several methods available in the ArrayList class (e.g. add, remove, isEmpty, contains, etc.).You can construct an ArrayList instance for managing your Point objects as follows:

              ArrayList<Point> path = new ArrayList<Point>();            

  Then, you can add new points to your path using the add(...) method of the ArrayList class as follows:

              Point p1 = new Point(x, y);            path.add(p1);            

• Signatures for the methods you must implement in your RandomWalk class. The methods are also defined in theRandomWalkInterface.Note that while you must implement the methods as defined by their signatures, you may also implement additional methods as needed.
  • public RandomWalk(int gridSize)Initializes the instance variables and adds the starting point of the walk, but doesnt create the entire walk. Instantiates a random number generator without a seed.
  • public RandomWalk(int gridSize, long seed)Same as the above constructor except that we specify a seed for the random number generator. This is very useful for debugging and testing as the same seed will give the same random number sequence so that we can reproduce a bug! This constructor illustrates the concept of method overloading.
  • public void step()Makes the walk go one more step. To add a step to your path, you will add the new Point to your ArrayList. A new step should be added to your path every time the method is called.If the step is the final step, set the value of the done instance variable to true to signal that you are done with the random walk.It should not take a step if the done variable is set to true.Note that you will walk North or East with equal probability (use the random number generator). If you are at one of the edges, then you may have only one direction in which you can walk. You can handle this case in multiple ways. For example, you can always pick one of North or East and then if you find you cannot go in that direction, just generate another random choice until you can move.
  • public void createWalk()Creates the entire walk in one call by internally using the step() method.
  • public boolean isDone()Returns the current value of the done variable. (Just returns the value of the variable. Does not actually check if the path is at the end, this happens in the step method.)
  • public int getGridSize()Returns the size of the grid.
  • public Point getStartPoint()Returns the starting point of the walk.
  • public Point getEndPoint()Returns the ending point of the walk.
  • public Point getCurrentPoint()Returns the current point of the walk.
  • public ArrayList<Point> getPath()Getter that returns a copy of the random walk path ArrayList.
  • public String toString()Returns the path as a nicely formatted string as shown below:

    [0,4] [0,3] [1,3] [1,2] [2,2] [3,2] [3,1] [4,1] [4,0]

Testing your RandomWalk class

Write a RandomWalkDriver class that does the following:

• Implement a main method that deals with the user input as follows:
  • Prompts the user for the grid size and checks to make sure that user enters a positive integer. If the entered value is invalid, ask the user to enter a different integer. Keep doing this until they enter a valid integer. You can do this with a loop.
  • Prompts the user for the random seed value and checks to make sure that the user enters a 0 or positive integer. If the entered value is invalid, ask the user to enter a different integer. Keep doing this until they enter a valid integer. You can also do this with a loop.
  • Creates a RandomWalk object with the appropriate constructor. If the seed is zero, then call the constructor with only grid size as an argument. Otherwise call the constructor with two arguments.
  • Create the walk using the createWalk() method and then print the walk (using the toString() method in theRandomWalk class).
• Hints on testing:
  • Test for bad input like negative or zero for grid size, negative random seed to make sure your program catches the error and asks user to enter values again and again until they get it right!
  • Test for boundary cases:
    • Try small values like 1, 2, 3, 4 for grid size to see if the path generated is correct.
    • Try random seed like 1234 and verify that you generate the same path each time.
    • Try random seed input of zero and verify that you get different random paths each time.
    • Try a few larger grid sizes like 10, 20, 100 to see if your program stops normally. It is hard to check if the output is correct for large grid size but using the GUI program will make it easier. Can you think of how to write a method that checks if the generated path is valid?
  • Use the RandomWalkGUI program to make it easier to debug your program!

Sample Session

java RandomWalkDriverEnter grid size:6Enter random seed (0 for no seed):1234[0,5] [0,4] [1,4] [1,3] [2,3] [2,2] [3,2] [4,2] [4,1] [5,1] [5,0]For the same grid size and same seed, we should get the same output even though it is random!java RandomWalkDriverEnter grid size:6Enter random seed (0 for no seed):1234[0,5] [0,4] [1,4] [1,3] [2,3] [2,2] [3,2] [4,2] [4,1] [5,1] [5,0]With a random seed of 0, we don't supply a seed to Random so the walk will be different each time we run the programjava RandomWalkDriverEnter grid size:8Enter random seed (0 for no seed):0[0,7] [1,7] [1,6] [1,5] [2,5] [2,4] [3,4] [4,4] [4,3] [5,3] [5,2] [6,2] [6,1] [6,0] [7,0]java RandomWalkDriverEnter grid size:8Enter random seed (0 for no seed):0[0,7] [1,7] [2,7] [2,6] [3,6] [4,6] [4,5] [4,4] [4,3] [5,3] [5,2] [5,1] [5,0] [6,0] [7,0]Now we show some error checking on the user supplied inputjava RandomWalkDriverEnter grid size:-5Error: grid size must be positive!Enter grid size:-6Error: grid size must be positive!Enter grid size:6Enter random seed (0 for no seed):-233Error: random seed must be >= 0!Enter random seed (0 for no seed):-455Error: random seed must be >= 0!Enter random seed (0 for no seed):1234[0,5] [0,4] [1,4] [1,3] [2,3] [2,2] [3,2] [4,2] [4,1] [5,1] [5,0]

Using the RandomWalkGUI class for testing and visualization

You can also use the provided RandomWalkGUI class (that uses the GridMap class) to see the results of your program in an animated form. Note that the RandomWalkGUI class expects your RandomWalk class to have properly implemented step(), isDone() and getPath() methods. The image shown above is a screenshot of the RandomWalkGUI program. You dont have to do anything to make the GUI work except implement the methods in the RandomWalk class as specified above!

Please note that the RandomWalkGUI uses command line arguments. So to use it, for example, you would type (on one line):

        java RandomWalkGUI 8 1234  

where 8 is the grid size and 1234 is the random seed. Note that you can skip the second input value (for the seed) and it would use the constructor without the seed and produce different random paths each time.

Using the RandomWalkUnitTester class for testing methods

When you are done, you can also run the RandomWalkUnitTester to check if your methods meet all the requirements. It will execute several tests on your RandomWalk class and provide PASS or FAIL output with feedback.