Understanding Java Records

Java 17 introduced records, a special kind of class designed to simplify the creation of immutable data carriers. Records reduce boilerplate code and provide a more concise way to define classes that primarily serve as data holders.

What are Records?

Records are intended for situations where a class is created solely to hold data. They automatically generate several key methods, including:

• Constructor: A constructor that initializes the fields
• Accessors: Getter methods for each field
• equals() and hashCode(): Implementations that compare records based on their field values
• toString(): A method that returns a string representation of the record's fields

Basic Record Example

record Book(String author, String title, double price) {
}

public class TestBook {
    public static void main(String[] args) {
        Book book = new Book("Morgan Housel ", "The Psychology of Money", 313);
        System.out.println("Details of the book : " + book);
        System.out.println(book.author());
        System.out.println(book.title());
        System.out.println(book.price());
        System.out.println("Hash code of Book" + book.hashCode());
    }
}

Output:

Details of the bookBook[author=Morgan Housel , title=The Psychology of Money, price=313.0]
Morgan Housel
The Psychology of Money
313.0
Hash code of Book:1015016633

Key Features of Records

• All fields in records are final, they cannot be modified
• Since values are immutable, there are no setter methods
• Records are final, they cannot be subclassed
• Records cannot extend from other classes as all records are implicitly inheriting from java.lang.Record and Java does not support multiple inheritance
• You can add instance methods to a record

Adding Custom Methods to Records

record Book(String author, String title, double price) {
    // Instance method to format book details in a specific way
    public String formattedDetails() {
        return String.format("'%s' by %s (Price: Rs.%.2f)", title, author, price);
    }
}

public class TestBook {
    public static void main(String[] args) {
        Book book = new Book("Morgan Housel", "The Psychology of Money", 313);
        
        // Using the formattedDetails() method
        System.out.println("Formatted Book Details: " + book.formattedDetails());
    }
}

Output:

Formatted Book Details: 'The Psychology of Money' by Morgan Housel (Price: Rs.313.00)

Benefits Over Traditional DTOs

Records significantly reduce boilerplate code associated with DTOs. Traditional DTOs require explicit constructors, getter methods, and implementations for equals(), hashCode(), and toString(). In contrast, records automatically generate these methods, making them more concise and easier to read. A record can replace a typical DTO class with just a single line of code.