Exercise Set 0

Question 0-1

Suppose we already have the following Topping class to represent a type of food that might go on top of a pizza.

public class Topping {
    public static final Topping PEPPERONI = new Topping(true);
    public static final Topping SAUSAGE = new Topping(true);
    public static final Topping ONION = new Topping(false);
    public static final Topping GREEN_PEPPER = new Topping(false);
    public static final Topping BLACK_OLIVE = new Topping(false);

    private boolean is_meat;

    private Topping(boolean in_is_meat) {
        is_meat = in_is_meat;
    }

    public boolean isVegetarian() {
        return !is_meat;
    }
}

Write a Pizza class that represents a pizza with up to 7 toppings. Your class should contain the following methods.

Pizza(): Constructs a pizza with no toppings.
void addTopping(Topping what): Adds the topping what onto the pizza.
boolean isVegetarian(): Returns true if all the toppings on the pizza are vegetarian.

Though it may appear that you need an array to store all the toppings, in fact there's a way to do this without an array.

To test your Pizza class, you can use the following program.

import csbsju.cs160.*;

public class PizzaTest {
    public static void main(String[] args) {
        Pizza p = new Pizza();
        p.addTopping(Topping.ONION);
        IO.println(p.isVegetarian()); // prints ``true''

        p.addTopping(Topping.GREEN_PEPPER);
        IO.println(p.isVegetarian()); // prints ``true''

        p.addTopping(Topping.PEPPERONI);
        IO.println(p.isVegetarian()); // prints ``false''

        p.addTopping(Topping.BLACK_OLIVE);
        IO.println(p.isVegetarian()); // prints ``false''
    }
}

Solution

Question 0-2

Write a Point class to represent a point in two-dimensional Cartesian space. The point class should support the following methods.

Point(): Constructs a point at location (0,0) in the Cartesian plane.
Point(double x, double y): Constructs a point at location (x,y) in the Cartesian plane.
void translate(double dx, double dy): Moves the point by (dx, dy). In traditional Cartesian coordinates, this would move it dx units to the right and dy units up.
double distanceTo(Point other): Computes the distance to other from the point asked. For example, if x is the point (0,0) and y is the point (3,4), then x.distanceTo(y) should return ((0-3)² + (0-4)²)^0.5 = 5.

You can use the following class to test your point.

import csbsju.cs160.*;

public class PointTest {
    public static void main(String[] args) {
        Point origin = new Point();
        Point pt = new Point(3, 4);

        IO.println(pt.distanceTo(origin)); // prints ``5.0''

        pt.translate(2, 8);
        IO.println(pt.distanceTo(origin)); // prints ``13.0''
    }
}

Solution

Question 0-3

In CSCI 160, there are two types of grades: quiz grades (out of 30) and regular grades. The lowest quiz grade is dropped in computing a student's total score. For example, if a student scored 30/35 and 24/35 on two labs and 20/30, 15/30, and 30/30 on three quizzes, the student's total score would be (30 + 24 + 20 + 30) / (35 + 35 + 30 + 30) = 104 / 130 = 80%, since the lowest score is dropped.

Write a class Student to accumulate a single student's grade. This class should have three methods.

double getTotal(): Returns the fraction of the points the student has scored so far, neglecting the quiz score.
void addQuizScore(int score): Inserts a score of score points of the possible 30 for a quiz.
void addRegularScore(int score, int possible): Inserts a score of score points of the possible possible into the student's total.

I should be able to execute the following class to test your Student class.

import csbsju.cs160.*;

public class StudentTest {
    public static void main(String[] args) {
        Student stud = new Student();
        stud.addRegularScore(30, 35);
        stud.addRegularScore(24, 35);
        stud.addQuizScore(20);
        stud.addQuizScore(15);
        stud.addQuizScore(30);
        IO.println(100.0 * stud.getTotal() + "%"); // prints ``80.0%''
    }
}

Solution