How can I access gets and sets in a sub class?

Question

In this application we have the Automovel class:

public class Automovel {
    private String marca;
    private String matricula;
    private String anoConstrucao;
    private Motor motor;
    private int preco = 0;
}

(with their builders, getters and setters) and there is a class called Motor that is an attribute of the Automovel class.

Motor Class:

private int potencia;

    public Motor() {}

    public Motor(int potencia){
        this.potencia = potencia;
    }

    public int getPotencia() {return this.potencia;}

    public void setPotencia(int potencia) {
        this.potencia = potencia
}

There are also 2 subclasses of this class (MotorEletrico and MotorCombustao):

Motor Elétrico:

public class MotorEletrico extends Motor {

    private int autonomia;
    public MotorEletrico() {}

    public MotorEletrico(int potencia, int autonomia) {
        super(potencia);
        this.autonomia = autonomia;
    }

    public int getAutonomia() {
        return autonomia;
    }

    public void setAutonomia(int autonomia) {
        this.autonomia = autonomia;
    }

}

Motor Combustão:

public class MotorCombustao extends Motor{

    private int cilindrada;
    private String combustivel;

    public MotorCombustao(){}

    public MotorCombustao(int potencia, int cilindrada, String combustivel){
        super(potencia);
        this.cilindrada = cilindrada;
        this.combustivel = combustivel;
    }

    public int getCilindrada(){
        return cilindrada;
    }

    public void setCilindrada(int cilindrada){
        this.cilindrada = cilindrada;
    }

    public String getCombustivel(){
        return combustivel;
    }

    public void setCombustivel(String combustivel){
        this.combustivel = combustivel;
    } 
}

I store a car with an X engine in an array of Automovel objects, but when I try to access the getters and setters of the subclass (MotorCombustao / MotorEletrico), only the gets and sets of the mother class (Motor) appears. My problem is that I can't access the getters and setters of the motor subclasses. Here's an example of what I tried:

Automovel arrayteste[] = new Automovel[49];

Motor motor1 = new MotorEletrico();
motor1.setPotencia(5);

Automovel automovel1 = new Automovel("Opel", "xx-12-xx", "2000", motor1, 2000);

arrayteste[0] = automovel1;

System.out.println(arrayteste[0].getMotor().getPotencia()); //Here, I can't Do .getAutonomia

Answer 1

You need to cast the reference of the parent class to the corresponding child class if you want to access a method which is not inherited from the parent class e.g. the method, getAutonomia() is not inherited from Motor and therefore, you need to cast the reference of Motor to MotorEletrico before you can access getAutonomia(). Some more useful code is given below:

public class Main {
    public static void main(String[] args) {
        Automovel arrayteste[] = new Automovel[2];
        Motor motor;

        motor = new MotorEletrico(5, 10);
        arrayteste[0] = new Automovel("Opel", "xx-12-xx", "2000", motor, 2000);

        motor = new MotorCombustao(7, 4, "xx-yy-zz");
        arrayteste[1] = new Automovel("Opel", "xx-08-xx", "1995", motor, 1995);

        for (Automovel automovel : arrayteste) {
            motor = automovel.getMotor();
            if (motor instanceof MotorEletrico) {
                System.out.println(((MotorEletrico) motor).getAutonomia());
            }
            if (automovel.getMotor() instanceof MotorCombustao) {
                System.out.println(((MotorCombustao) motor).getCilindrada());
                System.out.println(((MotorCombustao) motor).getCombustivel());
            }
        }
    }
}

Output:

10
4
xx-yy-zz

---

[Update: the following update is based on your comment]

Another way to iterate arrayteste is as given below:

for (int i = 0; i < arrayteste.length; i++) {
    if (arrayteste[i] != null) {
        motor = arrayteste[i].getMotor();
        if (motor instanceof MotorEletrico) {
            System.out.println(((MotorEletrico) motor).getAutonomia());
        }
        if (arrayteste[i].getMotor() instanceof MotorCombustao) {
            System.out.println(((MotorCombustao) motor).getCilindrada());
            System.out.println(((MotorCombustao) motor).getCombustivel());
        }
    }
}