Location class practice test solutions

Complete the Location class practice test before reviewing the solution.

Review the Location class practice test with AP CS Tutor Brandon Horn.

Question 1

new Location(4,0);

All GridWorld methods use Location objects, rather than individual row and column coordinates, to refer to locations. It is occasionally necessary to construct a Location object given a row and column to use one of the methods.

Question 2

Location.SOUTH

getAdjacentLocation takes an int representing a direction as a parameter. Although it is possible to pass in 180, you should use the Location class constants to make your code clearer.

Question 3

(B) loc2 will refer to a Location object representing (5, 0).

Although the resulting location is not valid in the grid, the Location class knows nothing about the grid. This becomes important when you need to use a location obtained from one of the methods in the grid, a common requirement. You must first check if the location is valid using the isValid method of Grid.

Question 4

(A) int

Directions in GridWorld are represented as integers. There is no Direction class in GridWorld.

Question 5

if(dir1 == Location.SOUTH)
    System.out.println("pirates");

Directions are represented as type int in the case study. int is a primitive types. Values of type int are compared using ==, not the equals method. The Location class constants are all of type int.

Question 6

if(loc5.equals(new Location(3,3)))
    System.out.println("treasure");

Objects are compared with the equals method, not ==. In order to check if a location matches a specific location, you should construct a Location object. Comparing the row and column values individually duplicates the functionality of an existing method (equals) and may not receive full credit.

Question 7

Location loc5 = new Location((int) (Math.random() * r), (int) (Math.random() * c));

See Generate random numbers with Math.random().

Question 8

int result = hunterLoc.compareTo(new Location(3,3));
if(result < 0)
    System.out.println("Keep going!");
else if(result > 0)
    System.out.println("Turn around!");
else
    System.out.println("You found it!");

The Location class implements the Comparable interface. The compareTo method orders locations in row major order, which is exactly the order described in this problem.

See compareTo on the AP CS A Exam.

Additional GridWorld resources