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.

Replace the Sunflower class with a lambda expression.

@FunctionalInterface
interface Flower {
    void bloom();
}

class Sunflower implements Flower {
    @Override
    public void bloom() {
        IO.println("bright yellow flower.");
    }
}

class Main {
    void bloomField(Flower flower) {
        for (int i = 0; i < 15; i++) {
            flower.bloom();
        }
    }

    void main() {
        Flower sunflower = new Sunflower();
        bloomField(sunflower);
    }
}

Challenge 2.

Add a new method to the Flower interface above while keeping the @FunctionalInterface annotation. What error does Java give you?

What errors do you see if you remove the annotation but still have lambdas in your code?

Challenge 3.

Change the lambda expression you used for the Flower interface to a method reference.

Challenge 4.

One of these snippets of code will throw a NullPointerException. The other will not. Which do you think will do which? Why do you think that is?

@FunctionalInterface
interface Screamer {
    void scream();
}

class Lemon {
    void grab() {
        IO.println("UNACCEPTABLE!");
    }
}

class Main {
    void main() {
        Lemon lemon = null;
        Screamer s = lemon::grab;
    }
}

@FunctionalInterface
interface Screamer {
    void scream();
}

class Lemon {
    void grab() {
        IO.println("UNACCEPTABLE!");
    }
}

class Main {
    void main() {
        Lemon lemon = null;
        Screamer s = () -> lemon.grab();
    }
}

Challenge 4.

You should have done this challenge before:

Make a method named promptGeneric which can prompt the user for information but, based on if what they typed is properly interpretable, can reprompt them.

As part of this make a Parser interface and at least two implementations: IntParser and DoubleParser.

If not, do so now. Then in either case replace the usages of IntParser and DoubleParser with method references.

// CODE HERE

class Main {
    // CODE HERE

    void main() {
        int x = promptGeneric(
            "Give me an x: ", new IntParser()
        );
        double y = promptGeneric(
            "Give me a floating point y: ", new DoubleParser()
        );
    }
}