Why is this an issue?

In Java 16 records are finalized and can be safely used in production code. Records represent immutable read-only data structure and should be used instead of creating immutable classes. Immutability of records is guaranteed by the Java language itself, while implementing immutable classes on your own might lead to some bugs.

One of the important aspects of records is that final fields can’t be overwritten using reflection.

This rule reports an issue on classes for which all these statements are true:

• all instance fields are private and final
• has only one constructor with a parameter for all fields
• has getters for all fields

Noncompliant code example

final class Person { // Noncompliant
  private final String name;
  private final int age;

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

  public String getName() {...}

  public int getAge() {...}

  @Override
  public boolean equals(Object o) {...}

  @Override
  public int hashCode() {...}

  @Override
  public String toString() {...}
}

Compliant solution

record Person(String name, int age) { }

Exceptions

No issue is raised when changing the class to a record could change its contract. This includes classes involved in Java serialization, such as classes implementing Serializable or Externalizable, classes declaring serialization methods like writeObject, readObject, readObjectNoData, writeReplace, or readResolve, and classes declaring serialPersistentFields.

final class Person implements java.io.Serializable { // Compliant
  private final String name;

  Person(String name) {
    this.name = name;
  }

  String getName() {
    return name;
  }
}

No issue is raised when the class, constructor, constructor parameters, fields, or getters are annotated with framework metadata that defines the class shape or binding contract. This includes metadata used by serialization, persistence, dependency-injection, or data-binding frameworks such as Jackson, Gson, Jakarta EE, Java EE, Lombok, Micronaut, and Spring.

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;

final class PersonDto { // Compliant
  private final String name;

  @JsonCreator
  PersonDto(@JsonProperty("full_name") String name) {
    this.name = name;
  }

  String getName() {
    return name;
  }
}

Resources

• Records specification