Effective Java Patterns: When to Use Records vs Classes
Aug 01, 2025 am 04:40 AM
Records are used when the data is immutable, only used to carry data without complex behavior; 2. Classes are used when encapsulation, mutable state, inheritance or verification logic is required; 3. Avoid adding instance fields to records or destroying immutability; 4. Records are suitable for DTO and return value encapsulation, and classes are suitable for scenarios containing business logic or life cycle management; 5. If the object is only data aggregation, use records, and if it is a behavioral object, use classes.
In Java, choosing between records and classes come down to understanding the intent behind your data structure. Since records were introduced in Java 16 (as a permanent feature), they've provided a concise way to model immutable data carriers—but they're not a replacement for classes in every scenario. Here's when to use each, based on practical design patterns and real-world usage.
? Use Records for Immutable Data Carriers
Records are ideal when you're modeling data that:
- Is immutable
- Has no behavior (or minimal behavior)
- Exists primarily to hold and transfer data
A record automatically generates:
- A constructor for all fields
-
equals(),hashCode(), andtoString()methods - Accessor methods (getters) for each field
public record Person(String name, int age) {}This single line replaces what would be 20 lines in a traditional class.
When to use:
- DTOs (Data Transfer Objects)
- POJOs with only fields and getters
- Method return types bundling multiple values
- Keys in maps or configurations
? If you find yourself writing a class that only holds data and doesn't have mutable state or complex logic, it's likely a perfect candidate for a record.
? Use Classes When You Need Behavior or State Control
Classes remain the right choice when you need:
- Encapsulation (private fields with controlled access)
- Mutable state
- Inheritance (though use sparingly)
- Validation logic in constructors/setters
- Lazy initialization or computed fields
- Multiple constructors with different logic
public class Person {
private final String name;
private final int age;
public Person(String name, int age) {
if (age < 0) throw new IllegalArgumentException("Age cannot be negative");
this.name = name;
this.age = age;
}
public boolean isAdult() {
return age >= 18;
}
// Getters, maybe setters if mutable
}When to use classes:
- Domain models with business logic
- Entities that evolve over time
- Objects requiring lifecycle management
- Cases where you need to hide internal representation
? Records can't have instance fields beyond the header, can't extend other classes, and are final by design—so they're inflexible for complex modeling.
? Don't Force Records Where They Don't Fit
Some anti-patterns to avoid:
Adding mutators to records
public record Person(String name, int age) { private String email; // ? Instance field not allowed public void setEmail(String email) { this.email = email; } // ? Breaks immutability }Using records for configuration with logic
If your "config" object validates inputs or changes behavior based on state, use a class.Overriding accessors just to add logic
You can override accessors in records, but doing so often signals you should use a class instead.- You're tired of writing boilerplate for DTOs
- The object's entire meaning is its data
- You need encapsulation, behavior, or lifecycle control
- Your model evolves or enforces invariants
? Best Practices Summary
| Scenario | Use |
|---|---|
| Pure data, immutable, transparent | ? Record |
| Need validation or side effects | ? Class |
| Want inheritance or polymorphism | ? Class |
| Bundling return values from a method | ? Record |
Frequent copying with -style methods |
? Record (no built-in with ) |
| Need lazy-compute or derived fields | ? Class |
?? Note: Records don't support
withmethods like Kotlin's data classes. If you need copy-and-modify patterns, a builder pattern in a class may be better.
Final Thoughts
Think of records as "data, not behavior" . They're not meant to replace classes but to eliminate boilerplate when you're modeling simple, immutable aggregates.
Use records when:
Use classes when:
Choosing correctly leads to cleaner, more maintainedable code. When in doubt, start with a record—if you need more control, reflector to a class. It's a safe evolution path.
Basically: if it's a bag of data, use a record. If it's an object with purpose, use a class.
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