Records (From Java 16, Enterprise Usage in 17)

Records are a special type of class designed to model immutable data carriers.

They reduce boilerplate code and make intent explicit:

This class is only for holding data.

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Why Records Were Introduced

Before records, creating a simple data class required:

• Fields
• Constructor
• Getters
• equals()
• hashCode()
• toString()

Example (Traditional Class):

public class User {
    private final String name;
    private final int age;

    public User(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() { return name; }
    public int getAge() { return age; }

    @Override
    public boolean equals(Object o) { /* boilerplate */ }

    @Override
    public int hashCode() { /* boilerplate */ }

    @Override
    public String toString() { /* boilerplate */ }
}

Record Syntax

public record User(String name, int age) { }

That’s it.

Java automatically generates:

• Private final fields
• Public constructor
• Getter methods (name(), age())
• equals()
• hashCode()
• toString()

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Records Are Immutable

Fields are:

• final
• Cannot be modified

User user = new User("Mohan", 30);

user.name = "New";  // ❌ Compilation error

Immutability provides:

✔ Thread safety
✔ Safer design
✔ Predictable behavior

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Custom Constructor (Validation)

You can add validation logic.

public record Account(String accountNumber, double balance) {

    public Account {
        if (balance < 0) {
            throw new IllegalArgumentException("Balance cannot be negative");
        }
    }
}

This is called a compact constructor.

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Custom Methods Allowed

Records can have methods.

public record Account(String accountNumber, double balance) {

    public boolean isActive() {
        return balance > 0;
    }
}

But records:

❌ Cannot have instance fields (other than components)
❌ Cannot extend other classes
✔ Can implement interfaces

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Records with Collections

public record Order(String orderId,List<String> items) { }

Important:

• The reference is immutable,
• but the List itself can still be modified.
• For full immutability:

  List.copyOf(items);

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When to Use Records

✔ DTOs
✔ API responses
✔ Event payloads
✔ Value objects
✔ Immutable configuration objects

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Records are immutable data carrier classes introduced in Java 16. They automatically generate constructor, getters, equals(), hashCode(), and toString(), reducing boilerplate and improving code readability.