Question

why is my code returning a null value at the last output ?
I it is supposed to return this: Auto MERCEDES C from Garage: TOP SERVICE (x2)
Actualy, the full output should be :
Auto FORD S-MAX from Garage: SPEEDY
Auto FORD FOCUS from Garage: SPEEDY
Auto MERCEDES C from Garage: TOP SERVICE
Auto MERCEDES C from Garage: TOP SERVICE

I know the problem is somewhere in my contructor that conctruct a copy of my object.
Thank you

public class Garage {

    //final String naam;
    String naam;

    public Garage (String n){
        this.naam = n;
        }
    public String getName(){
        return naam;
    }

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

    public String toString(){
        return ""+getName(); 

    }

}

public class Auto {

    //static final String brandName; 
    String brandName;
    Garage garage;

    public Auto(String mn){
        this.brandName = mn;

    }
    public Auto(Auto a){
        this.hashCode();
    }
    public Auto(String mn, Garage g){
        //this(mn);
        this.brandName = mn;
        this.garage = g;
    }

    public String getBranName(){
        return brandName;
    }
    public Garage getGarage(){
        return garage;
    }

    public void setGarage(Garage g){
        this.garage = g;
    }

    public String toString(){
        return "Auto "+getBranName()+" from Garage: "+getGarage();
    }

}


public class GarageTester {

    /**
     * @param args
     */
    public static void main(String[] args) {

        Auto auto = new Auto("FORD S-MAX");
        Garage garage = new Garage("SPEEDY");
        auto.setGarage(garage);

        System.out.println(auto);

        auto = new Auto("FORD FOCUS",garage);

        System.out.println(auto);

        auto =  new Auto("MERCEDES C", new Garage("TOP SERVICE"));

        System.out.println(auto);

        Auto kopie = new Auto(auto);

        System.out.println(kopie);

    }

}

Answer 1

You haven’t implemented your copy constrictor right in the Auto class.

public Auto(Auto a){
    this.hashCode();
}

As of now, it just calls the hashCode() method but doesn’t initialize the class attributes:

Please correct it as below:

public Auto(Auto a){
    this.brandName = a.brandName;
    this.garage = a.garage;
}

Once done then Auto kopie = new Auto(auto); statement will result into new class instance kopie with atributes copied from auto instance.