I am feel lost: req. 4) The initializeIdAndName method must set the User object id and definition fields according to the arguments passed, and then return the object.

Thank you Gellert. You got ahead of my thinking, I already wanted to ask about this User.this where what that .this means and User. In line 20, when I write:

interface DBObject {
        void DBObject initializeIdAndName(long id, String name) {
        }
    }

But there is some red and yellow errors. img> <img Version with static have only yellow errors, and this version pass the task: img> <img And I start thinking, for what there for is interface or this method, when is not used in line: 20.?

I.) I don't know the answer to everything...:) but I try to write some useful things. I'll send you my solution, compare it with your own. This was also accepted:)

public class Solution {
    public static void main(String[] args) throws Exception {
        System.out.println(Matrix.NEO);
        System.out.println(Matrix.TRINITY);
    }

    static class Matrix {
        public static DBObject NEO = new User().initializeIdAndName(1, "Neo");
        public static DBObject TRINITY = new User().initializeIdAndName(2, "Trinity");
    }

    interface DBObject {
        User initializeIdAndName(long id, String name);
    }

    static class User implements DBObject {
        long id;
        String name;

        public User initializeIdAndName(long id, String name) {
            this.id = id;
            this.name = name;
            return this;
        }

        @Override
        public String toString() {
            return String.format("The user's name is %s, id = %d", name, id);
        }
    }
}

II.) You can't have a method that is both 'void' and returns a value:

((static or not)) void DBObject initializeIdAndName(long id, String name); // error:  void <---> DBObject

((static or not)) void initializeIdAndName(long id, String name); // void method = it must have no return command

((static or not)) DBObject initializeIdAndName(long id, String name); //  it must have return command, and must return a DBObject type to the caller

III.) What you sent in the second picture, and which was supposedly accepted, in my opinion does not fulfil the original intention of the task: I think the original intent would be to inherit the non-static (and has no body) method from the DBObject interface into the User class, and make an implementation of the method in that class. (Like in my Solution.) But you wrote something else:

interface DBObject {
    static DBObject initializeIdAndName(long id, String name) {
        return new User();
    }
}

The static method of an interface is not inherited! I don't think they use them much. What the lessons teach us about, interfaces and their methods, are all non-static methods in interfaces. What you coded is a completely separate method in the interface, and a completely separate method in the User class. They just have the same name, a coincidence. In the User class, try writing @Override above the method! Really worth a try:) This is what it will give you: "error: method does not override or implement a method from a supertype" In other words: this "static DBObject initializeIdAndName()" method is never used. It is unnecessary to have it there, you may delete this method from the interface, the program will work without it.