Constructor overloading in Java - Mini Project: Build & Apply

Constructor overloading

📖 Scenario: You are creating a simple Java class to represent a Book in a library system. Books can be created with different details depending on what information is available.

🎯 Goal: Build a Book class with constructor overloading so you can create books with either just a title, or a title and an author.

📋 What You'll Learn

Create a Book class with two constructors

First constructor takes a String title only

Second constructor takes String title and String author

Store the values in instance variables

Add a method getDetails() that returns a string with the book's title and author (or 'Unknown' if author not given)

💡 Why This Matters

🌍 Real World

Constructor overloading is useful when you want to create objects with different sets of information, like creating user profiles with optional details.

💼 Career

Understanding constructor overloading helps you write flexible and readable code, a common requirement in software development jobs.

1

Create the Book class with a title

Create a class called Book with a private String variable called title. Add a constructor that takes a String title parameter and assigns it to the instance variable title.

Java

public class Book {
    private String title;
    
    // Your code here
}

Need a hint?

Remember to use this.title = title; inside the constructor to set the instance variable.

2

Add a second constructor with title and author

Add a private String variable called author to the Book class. Then add a second constructor that takes two parameters: String title and String author. Assign both parameters to their respective instance variables.

Java

public class Book {
    private String title;
    private String author;

    public Book(String title) {
        this.title = title;
    }

    // Your code here
}

Need a hint?

Constructor overloading means having more than one constructor with different parameters.

3

Add getDetails() method to show book info

Add a public method called getDetails() that returns a String. It should return the book's title and author in this format: "Title: [title], Author: [author]". If author is null, return "Unknown" instead of the author name.

Java

public class Book {
    private String title;
    private String author;

    public Book(String title) {
        this.title = title;
    }

    public Book(String title, String author) {
        this.title = title;
        this.author = author;
    }

    // Your code here
}

Need a hint?

Use a conditional expression to check if author is null.

4

Create Book objects and print details

In the main method, create two Book objects: one using the constructor with only title "Java Basics", and another using the constructor with title "Advanced Java" and author "John Doe". Then print the details of both books using the getDetails() method.

Java

public class Book {
    private String title;
    private String author;

    public Book(String title) {
        this.title = title;
    }

    public Book(String title, String author) {
        this.title = title;
        this.author = author;
    }

    public String getDetails() {
        String authorName = (author == null) ? "Unknown" : author;
        return "Title: " + title + ", Author: " + authorName;
    }

    public static void main(String[] args) {
        // Your code here
    }
}

Need a hint?

Create objects with new Book(...) and print using System.out.println().