30 Days of Code - Day 13: Abstract Classes

Coding challenges are a great resource for learning coding techniques and improve analytical thinking, this is a collection of challenges from different platforms.

Objective

Today, we’re taking what we learned yesterday about Inheritance and extending it to Abstract Classes. Because this is a very specific Object-Oriented concept, submissions are limited to the few languages that use this construct. Check out the Tutorial tab for learning materials and an instructional video!

Task

Given a Book class and a Solution class, write a MyBook class that does the following:

• Inherits from Book

• Has a parameterized constructor taking these 3 parameters:

  1. string title
  2. string author
  3. int price

• Implements the Book class' abstract display() method so it prints these lines:

1. Title:, a space, and then the current instance’s title.
2. Author:, a space, and then the current instance’s author.
3. Price:, a space, and then the current instance’s price.

Note: Because these classes are being written in the same file, you must not use an access modifier (e.g.: public) when declaring MyBook or your code will not execute.

Input Format

You are not responsible for reading any input from stdin. The Solution class creates a Book object and calls the MyBook class constructor (passing it the necessary arguments). It then calls the display method on the Book object.

Output Format

The void display() method should print and label the respective title, author, and price of the MyBook object’s instance (with each value on its own line) like so:

Title: $title
Author: $author
Price: $price

Note: The $ is prepended to variable names to indicate they are placeholders for variables.

Sample 00

The Alchemist
Paulo Coelho
248

Title: The Alchemist
Author: Paulo Coelho
Price: 248

Solution

package main

import (
  "bufio"
  "fmt"
  "os"
  "strconv"
)

func main() {
  s := bufio.NewScanner(os.Stdin)

  s.Scan()
  title := s.Text()
  s.Scan()
  author := s.Text()
  s.Scan()
  price, _ := strconv.Atoi(s.Text())

  book := NewMyBook(title, author, price)
  book.display()
}

type Book struct {
  title, author string
}

func (b Book) display() {
  fmt.Println("Implement the 'display' method!")
}

type MyBook struct {
  Book
  price int
}

func NewMyBook(title, author string, price int) MyBook {
  return MyBook{Book{title, author}, price}
}

func (b *MyBook) display() {
  fmt.Printf("Title: %v\nAuthor: %v\nPrice: %v\n", b.title, b.author, b.price)
}