What is @RequiredArgsConstructor used for?

@RequiredArgsConstructor generates a constructor that includes only the fields Lombok considers "required": final fields, and fields annotated @NonNull that don't already have a default value assigned.

@RequiredArgsConstructor
public class Person {
    private final String name;   //  required: included
    @NonNull
    private String email;        //  required: included
    private int age;             //  not required: excluded
}
//  generates: public Person(String name, String email) { ... }

This is especially common in Spring applications for constructor-based dependency injection: marking injected dependency fields as final and applying @RequiredArgsConstructor at the class level generates exactly the constructor Spring needs to inject those dependencies, without listing every other, non-dependency field.

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