Master Java Records: Simplify Immutable Classes in Java 16+

Declaring a record class

Since Java 16, the record keyword can be used to define a class, offering a concise way to create a final class. record range(int start, int end) {} Records can be declared in three ways:

In a separate file: public record range(int start, int end) {} Inside another class:

public class DidispaceTest {
    public record range(int start, int end) {}
}

Inside a method:

public class DidispaceTest {
    public void test() {
        public record range(int start, int end) {}
    }
}

Record class details

A record automatically provides:

It is a final class.

Implementations of equals, hashCode, and toString.

All component fields are public and immutable.

The previous range class is equivalent to:

public final class range {
    final int start;
    final int end;

    public range(int start, int end) {
        this.start = start;
        this.end = end;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        range range = (range) o;
        return start == range.start && end == range.end;
    }

    @Override
    public int hashCode() {
        return Objects.hash(start, end);
    }

    @Override
    public String toString() {
        return "range{" + "start=" + start + ", end=" + end + '}';
    }

    public int start() { return start; }
    public int end() { return end; }
}

To verify the generated methods, you can run a simple test:

@Test
public void test() {
    range r = new range(100, 200);
    log.info(r.toString());

    range r2 = new range(100, 200);
    log.info(String.valueOf(r.equals(r2)));
}

Defining member functions

Records can also contain custom methods. For example, adding a distance calculation:

record range(int start, int end) {
    int distance() {
        return end - start;
    }
}

Usage:

range r = new range(100, 200);
int d = r.distance();

For more Java new‑feature tutorials, see the free Java features series.