Construction of a class in java

Question

I should carry out this exercise in the creation of a class, I uploaded this is the professor's solution, in sum and product methods can not quite figure out what place and why use "A".

class Vettore {
    private int[] V = new int[6];
    public Vettore(int[] X) {
        if (X.length != 6)
            throw new BadDataException();
        for (int i = 0; i < 6; i++)
            if (X[i] < 0)
                throw new BadDataException();
            else
                V[i] = X[i];
    }
    public Vettore() {}
    public Vettore somma(Vettore X) {
        int[] A = new int[6];
        for (int i = 0; i < 6; i++)
            A[i] = V[i] + X.V[i];
        return new Vettore(A);
    }
    public Vettore prodotto(Vettore X) {
        int k = 0;
        for (int i = 0; i < 6; i++)
            k += V[i] * X.V[i];
        return k;
    }
    public int get(int i) {
        if (i < 0 || i > 5)
            throw new BadDataException();
        return V[i];
    }
    public String toString() {
        String t = "( ";
        for (int i = 0; i < 6; i++)
            t += V[i] + (i == 5 ? " " : ", ");
        return t + ")";
    }
    public boolean equals(Vettore X) {
        for (int i = 0; i < 6; i++)
            if (V[i] != X.V[i])
                return false;
        return true;
    }
}

Answer 1

As far as I see it, and assuming somma means sum and prodotto means product , The A is needed because you have to store the sum values of the V and XV arrays for every index . If you didn't use another array for this, you wouldn't be able to achive adding the appropriate indexes in somma for example. This method stands for - as I see it - Adding the two arrays' appropriate elements .

EDIT: another thing. Are you sure that the return types match variables to return? I elaborated the use of somma but didn't pay attention that prodotto has a wrong return type, just as it was said in the comments.

Answer 2

1. You might want to correct the prodotto method definition as -

    public Vettore prodotto(Vettore X) { int[] K = new int[6]; // deault values are 0 for (int i = 0; i < 6; i++) K[i] += V[i] * XV[i]; return new Vettore(K); } 

This would evaluate the product of the array field V for two instances of class Vettore namingly X the input param and the current instance that you would call the method from.

2. return new Vettore(K); creates a new instance of Vettore class with K as arrays field, while executing the constructor logic in place as follows -

    public SumAndProductExercise(int[] X) { if (X.length != 6) { // length of the array is 6 or not throw new BadDataException(); } for (int i = 0; i < 6; i++) { if (X[i] < 0) { // all the elements of array are >=0 or not throw new BadDataException(); } else { V[i] = X[i]; // the field on the new instance } } }