Lombok @Value annotation Examples

Lombok Value annotation (@Value) is used when creating Immutable classes. All Lombok generated fields are made  private and  final  by default, and setters are not generated. The class itself is also made final by default.

Make sure you already installed Lombok setup for your IDE. To Setup in Eclipse or in Spring Tool Suite refer to our Lombok Maven example setup with Eclipse.

1. What is Lombok @Value annotation?

@Value annotation is short hand for the annotation combination @Getter @FieldDefaults(makeFinal=true, level=AccessLevel.PRIVATE) @AllArgsConstructor @ToString @EqualsAndHashCode .

Following side by side code demonstrates simple usage of Lombok’s @Value annotation and how looks like Lombok generated code exactly when you use @Value annotation.

@Getter 
@FieldDefaults(makeFinal=true, level=AccessLevel.PRIVATE)
@AllArgsConstructor 
@ToString @EqualsAndHashCode
public final class User1 {
	
	private Long id;
	private String username;
}

@Value
public class User2 {

	private Long id;

	private String username;
}

Now let’s have a look into Lombok generated (Delomboked) code for both classes.

public final class User1 {
	private final Long id;
	private final String username;

	public Long getId() {
		return this.id;
	}

	public String getUsername() {
		return this.username;
	}

	public User1(final Long id, final String username) {
		this.id = id;
		this.username = username;
	}

	@Override
	public String toString() {
		return "User1(id=" + this.getId() + ", username=" + this.getUsername() + ")";
	}

	@Override
	public boolean equals(final Object o) {
		if (o == this)
			return true;
		if (!(o instanceof User1))
			return false;
		final User1 other = (User1) o;
		final Object this$id = this.getId();
		final Object other$id = other.getId();
		if (this$id == null ? other$id != null : !this$id.equals(other$id))
			return false;
		final Object this$username = this.getUsername();
		final Object other$username = other.getUsername();
		if (this$username == null ? other$username != null : !this$username.equals(other$username))
			return false;
		return true;
	}

	@Override
	public int hashCode() {
		final int PRIME = 59;
		int result = 1;
		final Object $id = this.getId();
		result = result * PRIME + ($id == null ? 43 : $id.hashCode());
		final Object $username = this.getUsername();
		result = result * PRIME + ($username == null ? 43 : $username.hashCode());
		return result;
	}
}

public final class User2 {
	private final Long id;
	private final String username;

	public User2(final Long id, final String username) {
		this.id = id;
		this.username = username;
	}

	public Long getId() {
		return this.id;
	}

	public String getUsername() {
		return this.username;
	}

	@Override
	public boolean equals(final Object o) {
		if (o == this)
			return true;
		if (!(o instanceof User2))
			return false;
		final User2 other = (User2) o;
		final Object this$id = this.getId();
		final Object other$id = other.getId();
		if (this$id == null ? other$id != null : !this$id.equals(other$id))
			return false;
		final Object this$username = this.getUsername();
		final Object other$username = other.getUsername();
		if (this$username == null ? other$username != null : !this$username.equals(other$username))
			return false;
		return true;
	}

	@Override
	public int hashCode() {
		final int PRIME = 59;
		int result = 1;
		final Object $id = this.getId();
		result = result * PRIME + ($id == null ? 43 : $id.hashCode());
		final Object $username = this.getUsername();
		result = result * PRIME + ($username == null ? 43 : $username.hashCode());
		return result;
	}

	@Override
	public String toString() {
		return "User2(id=" + this.getId() + ", username=" + this.getUsername() + ")";
	}
}

2. Lombok @Data vs @Value

The Lombok @Value and Lombok @Data both annotations generate boilerplate code related to POJO items, one key difference is @Value annotation is used to make your classes immutable. By seeing above examples we can notice following differences.

4. @Value staticConstructor

If you specify a staticConstructor name, then the generated constructor will be private, a static factory method is created to that other classes can use to create instances.

@Value(staticConstructor = "getInstance")
public class User3 {

	private Long id;

	private String username;
	
}

public final class User3 {
	private final Long id;
	private final String username;

	private User3(final Long id, final String username) {
		this.id = id;
		this.username = username;
	}

	public static User3 getInstance(final Long id, final String username) {
		return new User3(id, username);
	}

     // Rest of code same as delomboked User2.java
}

5. Lombok @Value ignore/exclude fields

@Value annotation alone not provide support for ignoring fields from generating getters or toString or equals and hashCode methods. Following example demonstrates how to exclude fields when you are using @Value annotation.

@Value
public class User4 {

	private Long id;

	@Getter(value = AccessLevel.NONE)
	private String username;
	
	@ToString.Exclude
	private boolean active;
	
	@EqualsAndHashCode.Exclude
	@ToString.Exclude
	private int role;
	
}

6. Lombok @Value and @Builder together with default values

Following example demonstrates how to use @Value and @Builder together and to set default values. Note that all-args constructor access level changed public to package.

import lombok.Builder;
import lombok.Builder.Default;
import lombok.Value;

@Builder @Value
public class User5 {

	private Long id;

	private String username;
	
	@Default
	private boolean active = true;
	
	@Default 
	private int role = 3;
	
}

Testing User5 :

public class User5Test {

	public static void main(String[] args) {
		
		User5 user5 = User5.builder().build();
		
		System.out.println("user5 => "+user5);
		
		User5 user51 = User5.builder()
				.active(false)
				.id(Long.valueOf(1))
				.role(4)
				.username("Peter")
				.build();
		
		System.out.println("user51 => "+user51);
	}
}

Output Results :

user5 => User5(id=null, username=null, active=true, role=3)
user51 => User5(id=1, username=Peter, active=false, role=4)

7. Making class and fields non final

It is possible to change default behavior of @Value to not make class and fields non-final using @NonFinal, but the class lost immutable nature.

@Value
@Setter
@NonFinal
public class User6 {

	private Long id;

	@NonFinal
	private String username;
	
	public final String defaultStatus = "inactive";
	
	public static int defaultRole = 2;
		
}

You can see delomboked code for this example at our GitHub repository.

Conclusion

We have covered in this article what is Lombok value annotation (@Value), how do we use it in java with a simple example by differentiating lombok generated code. You can refer Delombok Maven example to see how looks like lombok generated code for your Lomboked classes.

You can checkout source code from our github repository.

You might be interested in our other following Lombok Tutorials :

1. Lombok @Getter @Setter and lazy getters
2. Lombok @Builder
3. Lombok @Builder.Default
4. Lombok @Singular
5. Lombok @NonNull
6. Lombok Spring Boot example