Constructor chaining in Java - Mini Project: Build & Apply

Constructor chaining

📖 Scenario: Imagine you are creating a simple Java class to represent a Book in a library system. Each book has a title, author, and yearPublished. You want to practice how constructors can call each other to avoid repeating code.

🎯 Goal: You will build a Book class with three constructors. The constructors will use constructor chaining to reuse code and set default values when some information is missing.

📋 What You'll Learn

Create a Book class with three constructors

Use constructor chaining to call one constructor from another

Set default values for missing parameters using constructor chaining

Print the book details using a method

💡 Why This Matters

🌍 Real World

Constructor chaining helps reduce repeated code when creating objects with different levels of detail, common in real-world Java applications like library systems or inventory management.

💼 Career

Understanding constructor chaining is important for writing clean, maintainable Java code and is often asked in Java developer interviews.

1

Create the Book class with fields and a full constructor

Create a class called Book with three fields: String title, String author, and int yearPublished. Then write a constructor with parameters String title, String author, and int yearPublished that sets these fields.

Java

public class Book {
    String title;
    String author;
    int yearPublished;

    // Your code here
}

Need a hint?

Remember to declare the fields first, then create the constructor with the same parameter names and assign them to the fields using this.

2

Add a constructor with two parameters using constructor chaining

Add a second constructor to the Book class with parameters String title and String author. Use this(title, author, 0) to call the first constructor and set yearPublished to 0 by default.

Java

public class Book {
    String title;
    String author;
    int yearPublished;

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

    // Your code here
}

Need a hint?

Use this(...) inside the second constructor to call the first constructor with a default year.

3

Add a constructor with only title using constructor chaining

Add a third constructor to the Book class with only the parameter String title. Use this(title, "Unknown Author") to call the second constructor and set author to "Unknown Author" by default.

Java

public class Book {
    String title;
    String author;
    int yearPublished;

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

    public Book(String title, String author) {
        this(title, author, 0);
    }

    // Your code here
}

Need a hint?

Use this(title, "Unknown Author") to reuse the second constructor and set a default author.

4

Add a method to print book details and test all constructors

Add a method void printDetails() to the Book class that prints the book's title, author, and yearPublished. Then create a main method that creates three Book objects using each constructor and calls printDetails() on each.

Java

public class Book {
    String title;
    String author;
    int yearPublished;

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

    public Book(String title, String author) {
        this(title, author, 0);
    }

    public Book(String title) {
        this(title, "Unknown Author");
    }

    // Your code here
}

Need a hint?

Print the details in printDetails() using System.out.println. In main, create three books using each constructor and call printDetails() on each.