Challenges

Remember the rules for this are

• Try to use only the information given up to this point in this book.
• Try not to give up until you've given it a solid attempt

Challenge 1

Change this position class such that it doesn't only have an x and a y. It should also have a z.

Then add the following static methods. fromZ, fromXY, fromXZ, and fromYZ.

class Position {
    int x;
    int y;

    Position(int x, int y) {
        this.x = x;
        this.y = y;
    }

    static Position fromX(int x) {
        return new Position(x, 0);
    }

    static Position fromY(int y) {
        return new Position(0, y);
    }
}

class Main {
    void main() {
        var p1 = Position.fromXY(1, 2);
        IO.println("(" + p1.x + ", " + p1.y + ", " + p1.z + ")");

        var p2 = Position.fromYZ(1, 2);
        IO.println("(" + p2.x + ", " + p2.y + ", " + p2.z + ")");

        var p3 = Position.fromXZ(1, 2);
        IO.println("(" + p3.x + ", " + p3.y + ", " + p3.z + ")");

        var p4 = Position.fromZ(4);
        IO.println("(" + p4.x + ", " + p4.y + ", " + p4.z + ")");
    }
}

Challenge 2

Make a static method in the Maths class called quadraticFormula. It should take in an a, b, and c and run the quadradic formula on those values.

This formula will give you either one "real" solution, two real solutions, or two imaginary solutions.

For now just throw an exception if the solutions are imaginary and treat having one solution as having two solutions with the same value.

class Maths {
    // CODE HERE
}

class Main {
    void main() {
        var result = Maths.quadraticFormula(6, -17, 12);
        IO.println(result.solutionOne);
        IO.println(result.solutionTwo);
    }
}

Challenge 3

Update your code above to also communicate if a solution is imaginary. Use a boolean or an enum field on whatever class you wrote to hold both solutions for this.¹

Challenge 4

Make the following code compile. Do so first by changing one of the fields to static then by instead passing an extra argument to the static method.

class Keychain {
    final String[] keys;

    Keychain(String[] keys) {
        this.keys = keys;
    }

    boolean hasKey(String key) {
        for (int i = 0; i < keys.length; i++) {
            if (keys[i].equals(key)) {
                return true;
            }
        }
        return false;
    }
}


class Main {
    Keychain keychain = new Keychain(new String[] {
        "house",
        "car",
        "shed"
    });

    static void unlock(String thing) {
        if (keychain.hasKey(thing)) {
            IO.println("You have unlocked my " + thing);
        }
        else {
            IO.println("You don't have a key for my " + thing);
        }
    }
    
    void main() {
        unlock("house");
        unlock("car");
        unlock("shed");
        unlock("heart");
    }
}