Data classes using Records or Lombok

Data classes are your way to go when you want to store information, but they have been very tedious to create.

The problem

Imagine you have a simple data class called Cuboid that describes a geomatrical cuboid. It gets defined by three doubles:

• Width, called sizeX
• Height, called sizeY
• Depth, called sizeZ

Of course our Cuboid should also implement the equals, hashCode and toString methods.

Normally, we would now go ahead and write this:

import java.util.Objects;

public class Cuboid {
    private final double sizeX;
    private final double sizeY;
    private final double sizeZ;

    public Cuboid(double sizeX, double sizeY, double sizeZ) {
        this.sizeX = sizeX;
        this.sizeY = sizeY;
        this.sizeZ = sizeZ;
    }

    public double getSizeX() {
        return sizeX;
    }

    public double getSizeY() {
        return sizeY;
    }

    public double getSizeZ() {
        return sizeZ;
    }

    @Override
    public String toString() {
        return "Cuboid{" +
                "sizeX=" + sizeX +
                ", sizeY=" + sizeY +
                ", sizeZ=" + sizeZ +
                '}';
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Cuboid cuboid = (Cuboid) o;
        return Double.compare(cuboid.sizeX, sizeX) == 0 && Double.compare(cuboid.sizeY, sizeY) == 0 && Double.compare(cuboid.sizeZ, sizeZ) == 0;
    }

    @Override
    public int hashCode() {
        return Objects.hash(sizeX, sizeY, sizeZ);
    }
}

That’s 47(!) lines just for a tiny data class that doesn’t do anything besides storing 3 double values…

Solution 1 (Java 15+): Record classes

Java 15 introduced a new awesome feature called Records. By using them, we can narrow the complete code down to only one line:

public record Cuboid(double sizeX, double sizeY, double sizeZ) { }

Java automatically provides all methods that we had to implement ourselves in the above code! The only difference is that the getters are not called getSizeX() etc, but are simply called sizeX().

Solution 2: Lombok

When you cannot use Records because your users are still running Minecraft 1.8 (WTF) or didn’t update to Java 15+ yet, you can use the Lombok framework instead.

Just add Lombok to your project, e.g. when using maven:

<dependency>
	<groupId>org.projectlombok</groupId>
	<artifactId>lombok</artifactId>
	<version>1.18.20</version>
	<scope>provided</scope>
</dependency>

Now we can simply annotate our class with the @Data annotation:

import lombok.Data;

@Data
public class Cuboid {
    private final double sizeX;
    private final double sizeY;
    private final double sizeZ;
}

Once again, we got rid of defining constructors, getters and the hashCode, toString and equals method! Lombok will automatically generate all this stuff for you!

You can learn more about Lombok here – it has many other awesome features!