Can I use the Lombok @Builder passing the parent class as parameter?

Question

I want to create a new Child instance passing a Parent and other additional parameters.

For example if I have:

public class Parent {
    public String param1;
    public String param2;
    // many parameters
    public String paramN;
}

public class Child extends Parent {
    public String subValue;
}

With lombok, is there a builder that lets me create a Child instance passing the Parent and the missing value as parameters?

Would be easier if I could write something like:

Parent p = Parent.builder()
                 .param1("a")
                 .param2("b")
                 // many parameters
                 .paramN("b")
                 .build();
Child c = Child.builder(p).subValue("c").build();

Answer 1

Other answers don't truly make your client code simply reuse the parent instance you already have. But this is doable. You have two options:

The hard one is to write your custom annotation that does what you want. You can even make it generic so that it works for any classes the have parent/child hierarchy. Have a look at this example. If you feel brave you can raise a feature request on Lombok's github page.

Option two would be to write your custom builder for the child. See example here. In your custom builder in the init step you would be reading a passed in Parent instance, and setup the inherited fields only.