Add objects in ArrayList while designing class in Java

Question

I'm trying to create Patient and Allergy class and I'm confused about List allergies in setAllergies, whether it should be:

    this.allergies = allergies;

or

    allergies.add(allergies);

Patient class:

public class Patient {

    private List<Allergy> allergies;

    public List<Allergy> getAllergies() {
        return allergies;
    }

    public void setAllergies(List<Allergy> allergies) {
        this.allergies = allergies;
    }

}

Allergy class:

public class Allergy {
    private String name;
    private Severity severity;

    public Allergy(String name, Severity severity) {
        this.name = name;
        this.severity = severity;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Severity getSeverity() {
        return severity;
    }

    public void setSeverity(Severity severity) {
        this.severity = severity;
    }
}

allergies.add(allergies) makes no sense. It wouldn't even compile. — shmosel
– shmosel, Commented Jul 2, 2017 at 16:59
@shmosel The main confusion I do have is that Allergy class will return Allergy object then how is it getting added in the List<Allegry> by this.allergies = allergies ? From where the list of allergies will come from? As allergies is being passed as a parameter. — Nilesh Kumar
– Nilesh Kumar, Commented Jul 2, 2017 at 17:10

davidxxx · Accepted Answer · 2017-07-02 17:07:37Z

1

allergies.add(allergies);

adds a object to itself.
Why doing that ? Besides you cannot add a List to a List with add().
You have to use addAll() for that.

Actually the allergies field is null when a Patient instance is created.

As a consequence, doing it : allergies.invokeSomething(...); will throw a NullPointerException. Besides, the "set" prefix has a semantics to overwrite/replace, not to add.
So you should keep your method as you wrote for the moment :

public void setAllergies(List<Allergy> allergies) {
    this.allergies = allergies;
}

Now, if you want provide a way to add Allergies to the Allergies objects contained in the allergies field, you should provide a method addAllergies() :

public void addAllergies(List<Allergy> allergies) {
    this.allergies.addAll(allergies);
}

And you should also initialize the allergies field in its declaration (or in the constructor of Patient) :

private List<Allergy> allergies = new ArrayList<>();

edited Jul 2, 2017 at 17:07

answered Jul 2, 2017 at 16:55

davidxxx

132k23 gold badges231 silver badges228 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Nilesh Kumar Over a year ago

The main confusion I do have is that Allergy class will return Allergy object then how is it getting added in the List<Allegry> by this.allergies = allergies ? From where the list of allergies will come from? As allergies is being passed as a parameter.

davidxxx Over a year ago

"From where the list of allergies will come from? " You have provide as arguments the allergies List that you want to set in the Patient object.For example :

Patient p = new Patient(); List<Allergy> allergies = Arrays.asList(new Allergy(...), new Allergy(...)); p.setAllergies(allergies)

Nilesh Kumar Over a year ago

Got it. Thanks a lot.

Collectives™ on Stack Overflow

Add objects in ArrayList while designing class in Java

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related