[2018.12.27] Abstract Classes

Problem

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 Tutorialtab 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  parameters:
  1. string 
  2. string 
  3. int 
• Implements the Book class' abstract display() method so it prints these  lines:
  1. , a space, and then the current instance's .
  2. , a space, and then the current instance's .
  3. , a space, and then the current instance's .

Note: Because these classes are being written in the same file, you must not use an access modifier (e.g.: ) 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  method should print and label the respective , , and  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 Input

The following input from stdin is handled by the locked stub code in your editor:

The Alchemist
Paulo Coelho
248

Sample Output

The following output is printed by your display() method:

Title: The Alchemist
Author: Paulo Coelho
Price: 248

How I solved the problem

# 어제 다뤘던 Class를 상속받는 것과 비슷한 문제. super class가 어제는 일반 Class였다면 이번에는 Abstract Class(추상 클래스)임. 

import java.util.*;
 
abstract class Book {
    String title;
    String author;
    
    Book(String title, String author) {
        this.title = title;
        this.author = author;
    }
    
    abstract void display();
}
 
// Declare your class here. Do not use the 'public' access modifier.
    // Declare the price instance variable
class MyBook extends Book {
    int price;
 
    /**   
    *   Class Constructor
    *   
    *   @param title The book's title.
    *   @param author The book's author.
    *   @param price The book's price.
    **/
    // Write your constructor here
    
    MyBook (String title, String author, int price) {
        super(title, author);
        this.price = price;
    }
    /**   
    *   Method Name: display
    *   
    *   Print the title, author, and price in the specified format.
    **/
    // Write your method here
    public void display() {
        System.out.println("Title: " + title);
        System.out.println("Author: " + author);
        System.out.println("Price: " + price);
    }
}
// End class
 
public class Solution {
   
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String title = scanner.nextLine();
        String author = scanner.nextLine();
        int price = scanner.nextInt();
        scanner.close();
 
        Book book = new MyBook(title, author, price);
        book.display();
    }
}

[출처 : https://www.hackerrank.com ]