java how to share field and method between classes

Question

I have some BaseX pojo class ex:

public class Base1 {
    private String base1Field1;
    private String base1Field2;
    // getter & setter
}
public class Base2 {
    private String base2Field1;
    private String base2Field2;
    // getter & setter
}

And some DomainVo pojo class, it has some field & method from BaseX class ex:

//from base1
public class Domain1Vo {
    private String domain1Field1;
    private String base1Field1;
    private String base1Field2;
    // getter & setter
}
//from base1 & base 2
public class Domain2Vo {
    private String domain2Field1;
    private String base1Field1;
    private String base1Field2;
    private String base2Field1;
    private String base2Field2;
    // getter & setter
}

I don't want copy paste those fields from BaseX class to my domain object, but I can't use extends Base1, Base2 because java don't allow it.

I don't actually use BaseX in my code, I define them just want a single place to maintain those field.

update: I can't change my domain object structure, because it's come from/to other service as json. Also I need use it to generate a swagger doc(I use springfox). This why I need both field & method.

======== some research I did

I found a lib called lombok , it has a feature name @Delegate https://projectlombok.org/features/experimental/Delegate

//from base1
public class Domain1Vo {
    private String domain1Field1;
    @Delegate
    private Base1 base1;
    // getter & setter
}

It can generate method from BaseX class, but not field.

Answer 1

Composition is what you want. Inheritance is wildly overused (also getters and, especially, setters).

The base classes become components. (Use better names! Even "base" isn't a useful word to use in a class name.)

public final class Component1 {
    private String component1Field1;
    private String component1Field2;
    // domain methods
}
public final class Component2 {
    private String component2Field1;
    private String component2Field2;
}

public final class Domain1Vo {
    private String domain1Field1;
    private final Component1 component1;
    public Domain1Vo(
        Component1 component1
    ) {
        // Or construct.
        this.component1 =
           Objects.requireNonNull(component1);
    }
    // domain methods
}
//from base1 & base 2
public final class Domain2Vo {
    private String domain2Field1;
    private final Component1 component1;
    private final Component2 component2;
    public Domain2Vo(
        Component1 component1,
        Component2 component2,
    ) {
        // Or construct.
        this.component1 =
           Objects.requireNonNull(component1);
        this.component2 =
           Objects.requireNonNull(component2);
    }
    // domain methods
}