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Java Records

A record is a class for carrying data, and the compiler writes its common methods. The previous lesson wrote equals and hashCode by hand for a data class.

A record replaces the hand-written class

One header names the data. The printed form shows every field.

public class Main {
  public static void main(String[] args) {
    Student ana = new Student("Ana", 92);
    System.out.println(ana);
  }
}
record Student(String name, int score) {}

Accessors carry the component names

Each component gets an accessor with the same name. No get prefix appears.

public class Main {
  public static void main(String[] args) {
    Student ana = new Student("Ana", 92);
    System.out.println(ana.name());
    System.out.println(ana.score());
  }
}
record Student(String name, int score) {}

Equals and hashCode come for free

Two records with the same data compare equal. Their hash codes match too.

public class Main {
  public static void main(String[] args) {
    Student first = new Student("Ana", 92);
    Student second = new Student("Ana", 92);
    System.out.println(first.equals(second));
    System.out.println(first.hashCode() == second.hashCode());
  }
}
record Student(String name, int score) {}

Example

public class Main {
  public static void main(String[] args) {
    Student ana = new Student("Ana", 92);
    Student ben = new Student("Ben", 85);
    System.out.println(ana);
    System.out.println(ben);
    System.out.println(ana.equals(ben));
  }
}
record Student(String name, int score) {}

Key points

  • A record declares its data as components in its header.
  • The compiler writes a constructor, accessors, equals, hashCode and toString for a record.
  • A record prints every component by name and value.
  • Two records are equal when every component matches.
  • A record field cannot change after the record is made.

In this example, two records print in the same field form, and the different scores make equals answer false.

Note

A record suits plain data, not behaviour or changing state.

Try it Yourself

Edit the code, then press Run.

Running is simulated

Exercise

What does printing a record Student with name Ana and score 92 show?