CODEWITHSUNDEEP
javaoop
Masksway
Masksway

Reputation: 225

Understand how inheritance works in java

I'm learning oop, and I need to understand how inheritance actually works.

Let's say I have server call, with response that contain list of Movies, And another server call that I get the movie credits by movie id.

so my classes will look like this:

Class Movies :

public class Movies {
    private Movie[] movies;

   public Movies( Movie[] movies) {
        this.movies = movies;
    }
}

Class Movie:

public class Movie extends Movies {
    private String title;
    private int id;
    private int voteCount;

    public Movie(String title, int id, int voteCount) {
        super();//the problem
        this.title = title;
        this.id = id;
        this.voteCount = voteCount;
    } }

Class Credits:

public class Credits extends Movie {
     private int id; //movieId
       private Cast[] casts;


        public Credits(int id, Cast[] casts) {
            super();//the problem
            this.id = id;
            this.casts = casts;
        }

As you can see Credits extends Movie that extends from Movies.

The problem is for example Credits inherit from Movie, because Credits is part of a Movie, but when I extends Movie inside Credits and need to pass arguments to super() inside my constrcutor I don't really know what to do.

How can I get access to this arguments? why do I need to pass voteCount for example in my Credits` class to super constructor?

Upvotes: 1

Views: 78

Answers (1)

Jesper
Jesper

Reputation: 206996

You're using inheritance the wrong way. You have to understand what inheritance means. In programming, inheritance means specialization. It is not some arbitrary way to be able to access other parts of the program.

Which is to say: a subclass is a specialized version of its superclass.

Especially the "is a" is important. When you write:

public class Movie extends Movies

what you're really expressing is: "a Movie object is a (special kind of) Movies object", and

public class Credits extends Movie

"a Credits object is a (special kind of) Movie object".

You can already see that this doesn't make sense - a Movie is not a collection of Movie objects, and Credits are not some kind of Movie.

Theoretical explanation: Liskov substitution principle.

Upvotes: 1

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