Java parent's private attribute inside child constructor

Question

The title says it all, I got a class in which the variables of the constructor must be private.

public class AdMedia {
private String name;
private int price;

public AdMedia(){}


public AdMedia(String name, int price) {
    this.name = name;
    this.price = price;
}

that comes with public getter setter of the variables of course.

Now the problem comes right after I try to make a child class named Magazine. The class should inherit the name and price but the price is constant for every object initiation. so they won't be on the constructor as the name.

public class Magazine extends AdMedia {
private int area;
private String position;
private String topics;

public Magazine() {}
public Magazine(String name, int size, String position, String topic){

    super();
    this.size = size;
    this.position = position;
    this.topic = topic;

}

that also comes with its own getter setter too.

I try to put the price inside the constructor but the constructor demand a passed parameter. Using super(name) also notifies that none of parent constructor have such shape.

This complicates me when I'm trying to get the name using parent class method getName() which might require some downcasting I guess?

I had try to search for the solution but most require me to change the variable's accessibility into protected . Would there be no other way to do it in private ?

EDIT : I forgot to mention that the result by doing what I wrote above is the unability to access Magazine name, so when I try to downcast-get the name, what returned is a null.

Does this answer your question? [What is the difference between public, protected, package-private and private in Java?](https://stackoverflow.com/questions/215497/what-is-the-difference-between-public-protected-package-private-and-private-in) — WoAiNii, May 29 '20 at 16:45
what is the constant value of price ? Is it set by user who instantiates new Magazine() ? @DeanDebrio — QuickSilver, May 29 '20 at 17:04
@QuickSilver It supposed to be counted by the print amount, a variable in main, times £100 or something — Dean Debrio, May 29 '20 at 17:12
@WoAiNii I understand that private means the only one can access the variables is just the class, the parent, itself and cannot be inherited except by using parent's getter-setter. I'm actually confused at the part which I need to use the privates to a constructor that doesn't accept parameters of it (the 'price' variable). — Dean Debrio, May 29 '20 at 17:13

score 4 · Accepted Answer · answered May 29 '20 at 16:53

You could write your child constructor either as

public Magazine(String name, int size, String position, String topic){
    super();
    setName(name);
    setPrice(100); // 100 is your constant price
    this.size = size;
    this.position = position;
    this.topic = topic;
}

or as

public Magazine(String name, int size, String position, String topic){
    super(name, 100); // 100 is your constant price
    this.size = size;
    this.position = position;
    this.topic = topic;
}

Both ways would however open the possibility to change the price later:

Magazine m = new Magazine("name", 50, "position", "topic");
m.setPrice(10);

If you need to prevent this, you should also override the setPrice() setter:

public class Magazine extends AdMedia {

    ...
    @Override
    public void setPrice(int price) {
        // what to do here?
        // * you could either silently ignore 
        //   (which might surprise some users expecting to be able to change the price)
        // * throw an UnsupportedOperationException 
        //   (which might surprise other users which are not prepared to handle such an exception)
    }
}

Nevermind, the whole code fixed. I never used super like that before. Thanks! — Dean Debrio, May 29 '20 at 17:36

Java parent's private attribute inside child constructor

1 Answers1