Model design
- Java course
- Intermediate
- Lesson 65/116
- 6 min
Design the Post and Comment class skeleton.
Project: Blog app
In this five-lesson project you'll build a blog app. Each lesson adds one piece, and by the final lesson you'll complete a working mini command-line application.
You'll use what you learned in previous groups: classes, inheritance and List. First you'll design a Post class with title and author fields. Then you'll add a Comment class and link comments to posts.
The Comment class
Every blog post should accept comments. The Comment class is also a simple data holder like Post: it carries author and text fields. Both classes are written as POJOs (Plain Old Java Objects); fields are package-private and filled through a constructor.
For now we keep Comment separate from Post; the next lesson links them via a List<Comment>. Defining the two classes side by side is enough for now.
Practice Define the Post and Comment classes
Define class Post with String title and String author fields and a Post(String title, String author) constructor that assigns them. Define class Comment the same way with String author and String text fields and a Comment(String author, String text) constructor. In main, create a post with Post p = new Post("First post", "Ayşe"); and print its title with System.out.println(p.title);.
Starter code
// Define the Post class: title, author fields and constructor
// Define the Comment class: author, text fields and constructor
// main: create a Post instance and print its titleSample solution
class Post {
String title;
String author;
Post(String title, String author) {
this.title = title;
this.author = author;
}
}
class Comment {
String author;
String text;
Comment(String author, String text) {
this.author = author;
this.text = text;
}
}
public class Main {
public static void main(String[] args) {
Post p = new Post("First post", "Ayşe");
System.out.println(p.title);
}
}Expected output
First post
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is the role of the Post class?
- Read user input
- Delete comments
- Hold post data Correct answer
- Write to a file
Explanation: Post holds the data of a blog entry such as title and author.
2 Complete the constructor
class Post {
String title;
String author;
Post(String title, String author) {
this.title = title;
this.____ = author;
}
}class Post {
String title;
String author;
Post(String title, String author) {
this.title = title;
this.author = author;
}
}Explanation: this.author = author copies the parameter into the field.
3 Match the blog project concepts
| Term | Meaning |
|---|---|
Post |
Holds post data |
Comment |
Holds comment data |
title |
Post title |
author |
Post or comment writer |