"Constructor Album in class Album cannot be applied to different types"

Question

I'm currently having difficulty getting my new subclass to compile:

public class CompilationAlbum extends Album {

    private String seriesOfAlbums;

    public CompilationAlbum(String seriesOfAlbums) {
        this.seriesOfAlbums = seriesOfAlbums;
        albumType = "Compilation";
    }
}

Can anyone point out what I'm doing wrong? The fault seems to lie with the constructor, but I can't see why that should cause an error. The error message also reads "actual and formal argument lists differ in length."

EDIT: The Album class, minus methods, looks like this:

import java.util.ArrayList;

public class Album {

    private String name;
    private ArrayList<Track> trackList;
    private int length; 
    private int fileSize;
    private double averageRating;
    private String albumType;

    public Album(String name){
        this.name = name;
        trackList = new ArrayList<Track>();
    }

Following up on the conversation about how to set the name, I wouldn't consider the private fields to be a "problem." Assuming there are public or protected get/set methods, it would generally be preferable to use those (i.e. this.setName(name)) rather than directly modifying the fields. See some discussion about that here: http://stackoverflow.com/questions/2279662/java-protected-fields-vs-public-getters — Shaun, Nov 05 '14 at 19:01

Shaun · Answer 1 · 2014-11-05T17:06:42.557

2

If you don't explicitly call a constructor of the superclass in the first line of the subclass constructor, a call to super() is inserted by the compiler. Since Album doesn't have a no-argument constructor, compilation fails because the inserted call to super() isn't valid.

There are two ways to resolve this - either call the existing superclass constructor with some String argument (you'd have to decide what makes sense for your particular use case), or add a no-argument constructor to the superclass (again, the behavior of this constructor will depend on what you're actually trying to do).

Here's an approach that might make sense:

public class CompilationAlbum extends Album {

    private String seriesOfAlbums;

    public CompilationAlbum(String name, String seriesOfAlbums) {
        super(name);
        this.seriesOfAlbums = seriesOfAlbums;
        albumType = "Compilation";
    }
}

edited Nov 05 '14 at 17:06

answered Nov 05 '14 at 16:53

Shaun

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I've just edited my post to add the Album class (minus methods). – Zetland Nov 05 '14 at 16:58
Right - so that's what we thought. You'll fix the compilation error if you change the CompilationAlbum constructor to start with super(seriesOfAlbums); Alternatively, since that probably doesn't make sense in terms of your actual use case, you could add a no-argument constructor to Album. – Shaun Nov 05 '14 at 17:00
Okay, I've added `super(seriesOfAlbums);` and it works better now, although I'm still getting an error message for trying to construct `albumType` when `albumType` is a private variable. Do you know a way around this, allowing a subclass to modify its superclass? – Zetland Nov 05 '14 at 17:08

duffymo · Accepted Answer · 2014-11-06T10:37:31.500

Without seeing the source code for Album, I'm guessing that it does not have a default constructor.

You wrote this:

public class CompilationAlbum extends Album {

    private String seriesOfAlbums;

    public CompilationAlbum(String seriesOfAlbums) {
        this.seriesOfAlbums = seriesOfAlbums;
        albumType = "Compilation";
    }
}

You want this:

public class CompilationAlbum extends Album {

    private String seriesOfAlbums;

    public CompilationAlbum(String seriesOfAlbums) {
        super(seriesOfAlbums);
        this.seriesOfAlbums = seriesOfAlbums;
        albumType = "Compilation";
    }
}

Now that I see the Album class, your problem is private members. Make those protected so child classes can get at them, too.

I've just edited my post to add the Album class (minus methods). — Zetland, Nov 05 '14 at 16:59

"Constructor Album in class Album cannot be applied to different types"

2 Answers2