AGeekM's questions

Hello, I am comparing a vector with each one of the rows of a matrix. I have created a variable so that it indicates when it has reached the end of the vector so that it does not continue comparing. Said variable (called coincidence) I increase it every time I find a match but its value does not increase and I do not understand why. By not increasing, I don't get into the if that compares it with the length of the vector and keeps comparing me. Could someone point me to my mistake or give me a clue about the solution? Thanks in advance.

    int[][] matriz = {{2, 4, 6}, {1, 2, 4, 5, 5}, {1, 8, 9}};
    int[] vector = {2, 4, 5};

    int coincidencia = 0;


    for (int i = 0; i < matriz.length; i++) {
        for (int j = 0; j < matriz[i].length; j++) {

            if (vector.length  <= matriz[i].length ) {

                for (int k = 0; k < vector.length; k++) {

                    if (vector[k] == matriz[i][j]) {
                        System.out.println("Coincidencia en " + "[" + i + "]" + "[" + j + "]");
                        coincidencia++;
                        System.out.println(coincidencia);
                    } else {
                        coincidencia = 0;
                    }
                }
                if(coincidencia == vector.length) {
                    break;
                }
            } else{
                break;
            }
         }
    }

I am doing an exercise in Java to check if a vector is inside a matrix. In case the first position of the vector coincides with the current one of the array, I will jump to the next position of the vector to continue the check. My problem comes when it comes to skipping rows in the matrix and setting the position of the vector to 0. I don't know how to set this condition.

public static PosicionMatriz buscaVectorEnMatriz(int[][] matriz, int[] vector) {


    int coincidencia = 0;
    int avance  = 0;
    PosicionMatriz pm;
    int columna = 0;
    int fila = 0;


    vector = new int[3];
    vector[0] = 3;
    vector[1] = 5;
    vector[2] = 6;

    matriz = new int[3][3];
    matriz[0][0] = 1;
    matriz[0][1] = 5;
    matriz[0][2] = 3;
    matriz[1][0] = 3;
    matriz[1][1] = 5;
    matriz[1][2] = 6;
    matriz[2][0] = 2;
    matriz[2][1] = 9;
    matriz[2][2] = 0;



    for (int i = 0; i < matriz.length; i++) { // recorre el eje de la y
        for (int j = 0; j < matriz[0].length; j++) {// recorre el eje de la x
            for (int k = 0; k < vector.length; k++) { // recorre el vector

                if (vector.length > matriz[i].length) { // Si longitud de vector > que longitud de la fila pasa a la siguiente
                    coincidencia = 0;
                    i++; // Saltamos de fila
                }

                if (vector[k] == matriz[i][j]) {
                    coincidencia++;
                    System.out.println("Se ha encontrado la coincidencia en " + "[" + (i) + "]" + "[" + (j) + "]");

                } else {
                    k = 0; // Reestablecemos la posición del vector a la primera si no coincide con la de la matriz
                    coincidencia = 0;

                }

                if(coincidencia == vector.length) {
                    System.out.println("Finaliza la búsqueda");
                }
            }
        }
    }
    return null; 
}

Hello, I would like to know what is the difference between declaring int[] vector or declaring Integer[] vector. In a class exercise it has been declared in both ways and I don't know exactly what the difference is.

The JLS says that:

4.2. Primitive Types and Values

A primitive type is predefined by the Java programming language and named by a reserved word (§3.9): (...) Primitive values ​​do not share state with other primitive values. Numeric types are integral types and floating point types.

The integral types are byte, short, int, and long, whose values ​​are 8-bit, 16-bit, 32-bit, and 64-bit two's complement integers, respectively, (...) (§3.1).

The Integer Javadoc says:

The Integer class wraps the primitive type int in an object. An object of type Integer contains a single field whose value is of type int.

And of the arrays the JLS says :

Chapter 10. Arrays

In the Java programming language arrays are objects (§4.3.1), are created dynamically, and can be assigned to variables of type Object (§4.3.2). All methods of the Object class can be called on an array.

An array object contains a number of variables. The number of variables can be zero, in which case it is said to be an empty array. The variables contained in an array do not have names; instead they are referenced by array access expressions that use non-negative integers as index values. These variables are called components of the array. If an array has n components, we say that n is the length of the array; array components are referenced using integer indices from 0 to n-1, inclusive.

But that doesn't make clear to me the difference between int[] and Integer[]

I am doing an electronic messaging exercise with different classes and applying inheritance.

I would like to know how to solve the following method: isMember(...): a contact identifier is passed as a parameter (I already have it done in the main class with a method called getId) and it returns true if it is contained in the group (directly or indirectly), and false, if not found.

My main problem is not knowing how to compare each id with those that make up a group (class on which I am working).

Thanks in advance.

Hi, it may seem like a silly question but I am creating a method that passes an integer as a parameter and when it matches the position of a vector, it returns the value in that position. What would be the correct syntax? Thanks in advance.