CODEWITHSUNDEEP
javainheritance
Hauptman Koening
Hauptman Koening

Reputation: 69

parent and child same variable name,inheritance

if i have a class Fish

public class Fish {
int numberOfFins;
int age;
public Fish(int age){
    this.age=age;

}}

and class Shark that extends the Fish class

public class Shark extends Fish{
private int age;

public Shark(int age) {
    super(age);
    this.age=age;
}}

what age variable is accessed trough keyword this - is it of parent or from child class?

Thanks in advance?

Upvotes: 0

Views: 1910

Answers (3)

T.J. Crowder
T.J. Crowder

Reputation: 1074168

Which age you access depends on the type of the thing you use to access it. this always has the type of the class the method or constructor belongs to — that is, in Fish's methods/constructors, this is of type Fish. In Shark's methods/constructors, this is of type Shark. (There's only one object, which combines the features of Fish and Shark [yes, it really has two separate fields with the same name]; what we're talking about is the type of the reference to it.)

(Note that this is different for instance variables (like age; aka "fields") than it is for instance methods. In Java, methods are polymorphic, instance variables are not.)

So within Fish code, this.age is Fish's age. Within Shark code, this.age is Shark's age.

E.g.:

public class Fish {
    int numberOfFins;
    int age;
    public Fish(int age) {
        this.age=age;         // Sets Fish#age
    }
}

public class Shark extends Fish {
    private int age;

    public Shark(int age) {
        super(age);
        this.age=age;         // Sets Shark#age
    }
}

This doesn't only apply to this, it applies to variables as well. Look at main below (and notice that I set the two ages to different values; Shark's age is twice Fish's age):

class Fish {
    int numberOfFins;
    int age;
    public Fish(int age) {
        this.age = age;         // Sets Fish#age
    }
}

public class Shark extends Fish {
    private int age;

    public Shark(int age) {
        super(age);
        this.age = age * 2;     // Sets Shark#age
    }

    public static void main(String[] args) {
        Shark s = new Shark(10);
        Fish f = s;
        System.out.println(f.age); // 10
        System.out.println(s.age); // 20
    }
}

Upvotes: 3

Amer Qarabsa
Amer Qarabsa

Reputation: 6574

age will be inhereted from Fish but since you are decalring another variable with name "age" the inhereted variable will be hidden so what you will be having in your current object which is referenced by this is the variable declared in Shark

Upvotes: 0

Naman
Naman

Reputation: 31868

this

Within an instance method or a constructor, this is a reference to the current object — the object whose method or constructor is being called.

public Fish(int age){
    this.age=age; / the one is Fish
}

Similarly in the other class, you have a member with the same name, which would be referenced in its c'tor :

public Shark(int age) {
    super(age);
    this.age=age; // the one in class Shark
}

Upvotes: -1

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