Lombok @NoArgsConstructor, @RequiredArgsConstructor @AllArgsConstructor Annotations
This is a sample application of Lombok ‘s constructor generation below annotation.
@NoArgsConstructor(lombok.NoArgsConstructor)@AllArgsConstructor(lombok.AllArgsConstructor)@RequiredArgsConstructor(lombok.RequiredArgsConstructor)
Generate default constructor
@NoArgsConstructorYou can automatically generate the default constructor by giving it to the class.
■ Class that gave @ NoArgsConstructor
import lombok.NoArgsConstructor;@ NoArgsConstructor public class Person1 { private long id; private String name; private int age;}
■ Actually generated source code
The source code actually generated is as follows ( confirmed by delombok )
You can see that the default constructor is generated.
Public Class Person1 { Private Long Id; Private String Name; Private Int Age; public Person 1 () { }}
Generate a constructor for setting all members
@AllArgsConstructorBy assigning a class to a class, you can automatically generate a constructor with arguments to set values for all members.
■ Class that granted @ AllArgsConstructor
import lombok.AllArgsConstructor;@ AllArgsConstructor public class Person2 { private long id; private String name; private int age;}
■ Actually generated source code
The source code actually generated is as follows ( confirmation with delombok )
It turns out that a constructor with argument for setting all members is generated.
Public Class Person2 { Private Long Id; Private String Name; Private Int Age; Public Person2 ( Final Long Id, Final String Name, Final Int Age) { This .Id = Id; This .Name = Name; This .Age = Age; }}
@ NoArgsConstructor + @ AllArgsConstructor
@NoArgsConstructor@AllArgsConstructorBy assigning and to the class, it is possible to automatically generate both the default constructor and the constructor with arguments for setting values to all members.
■ Classes with @ NoArgsConstructor and @AllArgsConstructor
import lombok.AllArgsConstructor; import lombok.NoArgsConstructor;@ NoArgsConstructor @ AllArgsConstructor public class Person3 { private long id; private String name; private int age;}
■ Actually generated source code
The source code actually generated is as follows ( check with delombok )
You can see that the constructor with argument for setting the default constructor and all members is generated.
Public Class Person3 { Private Long Id; Private String Name; Private Int Age; public Person 3 () { } Public Person3 ( Final Long Id, Final String Name, Final Int Age) { This .Id = Id; This .Name = Name; This .Age = Age; }}
Generate a constructor that sets values to mandatory members
@RequiredArgsConstructorBy assigning a class to a class, you can automatically generate a constructor with arguments to set the value to a required member (final member).
■ Class with @ RequiredArgsConstructor
import lombok.RequiredArgsConstructor;@ RequiredArgsConstructor public class Person4 { private final long id; private String name; private int age;}
■ Actually generated source code
The actual source code generated is as follows ( confirmed by delombok )
A constructor for setting the value to final member (id) is generated.
Public Class Person4 { Private Final Long Id; Private String Name; Private Int Age; public Person 4 ( final long id) { this. id = id; }}
@ RequiredArgsConstructor + @ AllArgsConstructor
@RequiredArgsConstructorBy @AllArgsConstructorassigning and to the class, it is possible to automatically generate both the constructor for setting the value to the mandatory member and the constructor for setting the value to all the members.
■ Class with @ RequiredArgsConstructor and @AllArgsConstructor
import lombok.AllArgsConstructor; import lombok.RequiredArgsConstructor;@ RequiredArgsConstructor @ AllArgsConstructor public class Person 5 { private final long id; private String name; private int age;}
■ Actually generated source code
The source code actually generated is as follows ( confirmed by delombok )
You can see that the constructor that sets the value to the mandatory member and the constructor to set all the members are generated.
Public Class Person5 { Private Final Long Id; Private String Name; Private Int Age; public Person 5 ( final long id) { this. id = id; } Public Person5 ( Final Long Id, Final String Name, Final Int Age) { This .Id = Id; This .Name = Name; This .Age = Age; }}
Control access level of constructor
If you use annotations to generate a constructor, by default the access level of the constructor is public. If you want to control this access level, accessuse the parameter.
■ Sample code
Import Lombok.AccessLevel; Import Lombok.NoArgsConstructor; Import Lombok.RequiredArgsConstructor;public class Person 6 { @ NoArgsConstructor (access = AccessLevel.PRIVATE) public static class Person6a { private long id; private String name; private int age; } @ RequiredArgsConstructor (access = AccessLevel.PROTECTED) public static class Person 6b { private final long id; private String name; private int age; }}
■ Actually generated source code
In fact the source code that is generated is less than ( Delombok check)
is the private constructor of the access level of Person6a, constructor of the access level of Person6b you can see that has become protected.
public class Person 6 { public static class Person6a { private long id; private String name; private int age; private Person 6 a () { } } public static class Person6b { private final long id; private String name; private int age; protected Person 6b ( final long id) { this. id = id; } }}
Define a factory method
Sometimes you may want to call the factory method without calling the constructor directly.
In such cases, you staticNamecan define factory methods by using parameters.
■ Sample code
Import Lombok.AllArgsConstructor; Import Lombok.NoArgsConstructor; Import Lombok.RequiredArgsConstructor;public class Person 7 { @ RequiredArgsConstructor (staticName = "of" ) public static class Person7a { private final long id; private String name; private int age; } @ NoArgsConstructor (staticName = "create" ) @ AllArgsConstructor (staticName = "create" ) public static class Person 7 b { private long id; private String name; private int age; }}
■ Actually generated source code
You can see that the factory method with the name you specified is defined in the source code actually generated ( confirmation with delombok ) staticName. You can also see that the constructor is private.
public class Person 7 { public static class Person7a { private final long id; private String name; private int age; private Person 7 a ( final long id) { this. id = id; } public static Person 7 a of ( final long id) { return new Person 7 a (id); } } public static class Person7b { private long id; private String name; private int age; private Person 7b () { } public static Person 7 b create () { return new Person 7 b (); } Private Person7b ( Final Long Id, Final String Name, Final Int Age) { This .Id = Id; This .Name = Name; This .Age = Age; } public static Person 7 b create ( final long id, final String name, final int age) { return new Person 7 b (id, name, age); } }}
Combine with @ NonNull
If you simply grant @RequiredArgsConstructoror @AllArgsConstructorto a class that has a required member (final member), you can allow null to be set for the target member.
If you can not tolerate null members, @NonNulllet’s combine annotations.
■ Sample code
Import Lombok.AllArgsConstructor; Import Lombok.NonNull; Import Lombok.RequiredArgsConstructor;public class Person 8 { @ RequiredArgsConstructor public static class Person8a { private long id; @ NonNull private final String name; private int age; } @ AllArgsConstructor public static class Person 8 b { private final long id; @ NonNull private final String name; @ NonNull private final String description; }}
■ Actually generated source code
The source code actually generated is as follows ( confirmed with delombok )
You can see that null is guarded in the constructor’s processing.
import lombok.NonNull;public class Person 8 { public static class Person8a { private long id; @NonNull private final String name; private int age; public Person 8 a ( @ NonNull final String name) { if (name == null ) { throw new NullPointerException ( "name" ); } this .name = name; } } @ public static class Person8b { private final long id; @ NonNull private final String name; @ NonNull private final String description; Public Person8b ( Final Long Id, AttoNonNull Final String Name, AttoNonNull Final String Description) { If (Name == Null ) { Throw New NullPointerException ( "Name" ); } if (description == null ) { throw new NullPointerException ( "description" ); } This .Id = Id; This .Name = Name; This .Description = Description; } }}
Annotate the constructor
If you are using a DI container and want to do constructor injection, @Injectannotate the constructor .
In this way, if you want to add some annotation to the constructor, onConstructoruse the parameter.
Parameters are described as follows.
onConstructor=Atto__ ({ @Inject })
■ Sample code
onConstructorIt specifies that @Injectannotation should be given by parameter .
import javax.inject.Inject;import lombok.AllArgsConstructor; import lombok.RequiredArgsConstructor;public class Person 9 { AttoRequiredArgsConstructor (OnConstructor = Atto__ ({ @Inject })) public Static class Person9a { private long id; private final String name; private int age; } AttoAllArgsConstructor (OnConstructor = Atto__ ({ @Inject })) public Static class Person9b { private final long id; private final String name; private int age; }}
■ Actually generated source code
The source code actually generated is as follows ( confirmed with delombok ) You can see that the annotation is given to the
constructor @Inject.
import javax.inject.Inject;public class Person 9 { public static class Person9a { private long id; private final String name; private int age; AttoInject Public Person9a ( Final String Name) { This .Name = Name; } } public static class Person 9 b { private final long id; private final String name; private int age; @Inject public Person9b ( final long id, final String name, final int age) { this .id = id; this .name = name; name; this .age = age; } }}
