CODEWITHSUNDEEP
javaabstract-class
FatDog
FatDog

Reputation: 153

Subclass editing declared abstract classes classmember

I have an abstract class that subclasses will inherit. I want to have a get method that returns the amount of passengers. I declare this method in the abstract class and it will return the passengers.

The class member passengers is not defined but instantiated, so the get method knows what variable to return.

In the subclasses, I want this variable to have different values.

However, the get method returns 0 even when the amount of passengers is not 0.

I have tried writing: passengers = random.nextInt(4) + 1;

Abstract class vehicle

import java.util.Random;

public abstract class Vehicle {
    protected Random random = new Random();
    protected int passengers;

    public int getPassengerAmount() {
        return this.passengers;
    }
}

Class Car

public class Car extends Vehicle {
    private String name = "Car";
    private int size = 1;
    public int passengers = random.nextInt(4) + 1;
}

Upvotes: 2

Views: 114

Answers (4)

Hassam Abdelillah
Hassam Abdelillah

Reputation: 2294

You are not using the good approach to calculate how many passengers are in a certain vehicle.

It's nice to have your Vehicle as an abstract class as it will have only common caracteristic that all Vehicle share and let the specificities of each one being implemented in their respective classes.

For the Car. You have to implement your specific conception of how many passengers should be in a Car. Thus, getPassengerAmount() should be declared abstract in your Vehicle and be implemented in each specific vehicle.

That means :

import java.util.Random;

public abstract class Vehicle {
protected Random random = new Random();
protected int passengers;

public Vehicle() {
   initializeVehiculeOptions();  
}

public abstract int initializeVehiculeOptions();    
}

and

import java.util.Random;

public class Car extends Vehicle {

     private String name = "Car";
     private int size = 1;

     public Car() {
          super();
     }

     @Override
     public int initializeVehiculeOptions() {
          // Here you initialize for 
          this.passengers = random.nextInt(4) + 1;
     }
}

You will use a Car instance

Car ford = new Car();

Upvotes: -1

lainatnavi
lainatnavi

Reputation: 1613

public class Car extends Vehicle {
    private String name = "Car";
    private int size = 1;
    public int passengers = random.nextInt(4) + 1; // this is not passengers of the superclass
    void setPassengers() { passengers = random.nextInt(4) + 1; } // this is passengers of the superclass
}

Upvotes: 0

Farrukh
Farrukh

Reputation: 183

The answer to your question will be that you are initializing passengers variable directly. you have to create a constructor for it and assign a default value there. plus there is no need for you to create a public variable again in the subclass otherwise the abstract class makes no sense of existing. Note, an abstract class must have an abstract function.

Upvotes: 0

AntoineB
AntoineB

Reputation: 4694

You are masking the parent variable by redeclaring the passengers variable in the Car class.

You should initialize the parent variable in the constructor of the child instead:

public class Car extends Vehicle {

    private String name = "Car";
    private int size = 1;

    public Car() {
        this.passengers = random.nextInt(4) + 1;
    }

}

If you want it to be public, then you should make it public in the Vehicle class, but to be honest I wouldn't recommend it and I would rather go with protected variables but public getters / setters.

Upvotes: 2

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