Lombok @NoArgsConstructor examples

1. Generating no-args/default constructor using Lombok

Lombok @NoArgsConstructor will generate a no arguments/default constructor, by default generated constructor will be public.

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.

@NoArgsConstructor
public class NoArgsDemo1 {

	private Long id;
	
	private String username;
}

public class NoArgsDemo1 {
	private Long id;
	private String username;

	public NoArgsDemo1() {
	}
}

2. @NoArgsConstructor vs static and final fields

You will get a compiler error if class has any non initialized final fields. You need to set attribute value force=true if you have any non initialized final fields and all non initialized final fields set to their default values within generated constructor. static fields are not initialized within generated constructor for @NoArgsConstructor.

@NoArgsConstructor(force = true)
public class NoArgsDemo2 {

	private final Long id;
	
	private final String username;
	
	private final double minSalary;
	
	private final int defaultRole = 1;
	
	private static boolean status;
}

public class NoArgsDemo2 {
	private final Long id;
	private final String username;
	private final double minSalary;
	private final int defaultRole = 1;
	private static boolean status;

	public NoArgsDemo2() {
		this.id = null;
		this.username = null;
		this.minSalary = 0.0;
	}
}

3. No-args constructor with non-null fields

Like @AllArgsConstructor generates check for the non-null fields (fields declared as @NonNull), no check is generated for @NoArgsConstructor

@NoArgsConstructor
public class NoArgsDemo3 {

	private Long id;

	@NonNull
	private String username;
}

public class NoArgsDemo3 {
	private Long id;
	@NonNull
	private String username;

	public NoArgsDemo3() {
	}
}

4. Generating private no-args/default constructor

Lombok generates a public no-args constructor by default for the @NoArgsConstructor. To generate private no-args constructor declare @NoArgsConstructor(access = AccessLevel.PRIVATE). access attribute of @NoArgsConstructor allows you to change the access modifier of the generated constructor.

@NoArgsConstructor(access = AccessLevel.PRIVATE)
public class NoArgsDemo4 {

	private Long id;

	private String username;
}

public class NoArgsDemo4 {
	private Long id;
	private String username;

	private NoArgsDemo4() {
	}
}

5. Creating a static factory method using @NoArgsConstructor

@NoArgsConstructor(staticName = "getInstance") generates a static factory method named with getInstance, staticName attribute of @NoArgsConstructor allows us to generates a private no-args constructors and an additional static factory method that wraps around the private constructor is generated.

@NoArgsConstructor(staticName = "getInstance")
public class NoArgsDemo5 {

	private Long id;

	private String username;
}

public class NoArgsDemo5 {
	private Long id;
	private String username;

	private NoArgsDemo5() {
	}

	public static NoArgsDemo5 getInstance() {
		return new NoArgsDemo5();
	}
}

6. Put annotations on generated no-args constructor

Sometimes you may want to define annotations on top of constructor, for example when you are working with Spring framework or some other third part java libraries, you may need to declare annotations on top of constructor . onConstructor attribute of @AllArgsConstructor allows us to put annotations on generated all-args constructor.

1. Up to JDK7: @NoArgsConstructor([email protected]__({@AnnotationsGoHere}))
2. From JDK8: @NoArgsConstructor(onConstructor_={@AnnotationsGohere}) // note the underscore after onConstructor.

@NoArgsConstructor(onConstructor_= @Deprecated )
public class NoArgsDemo6 {

	private Long id;

	private String username;
}

public class NoArgsDemo6 {
	private Long id;
	private String username;

	@Deprecated
	public NoArgsDemo6() {
	}
}

7. Conclusion

In this guide we have covered Lombok NoArgsConstructor examples with several options. You can refer Delombok Maven example to see how looks like lombok generated code for your Lomboked classes.

You can checkout source code at github.

You might be interested in our other following Lombok Tutorials :

1. Lombok @Getter @Setter and lazy getters examples
2. Lombok @Data
3. Lombok @Value
4. Lombok @Builder
5. Lombok @NonNull
6. Lombok @Slf4j
7. Lombok @Singular
8. Lombok Spring Boot Example