Getting the same random number

Question

I want to generate a random number to apply to some arrays in order to get different elements in each execution. The arrays contain names of sport products (product,size,price,etc). By doing this, I want to make random products that would go into a String, but in each execution of the program, I get the same product.

Where is the problem?

Here is the code in the class generaProductos:

public void generaProductos() {
    int num;
    for (int i=0;i<3;i++){
        num = (int) Math.random() * 3;
        String cliente = tipoProducto[num] + " " + deporte[num] + " " +
                         destinatario[num] + " " + color[num] + " " + tallaRopaAdulto[num]
                         + " " +   preciosIVA[num];
        System.out.println(cliente);
     }
     return;
 }

And here is where I call generaProductos() method in main:

switch (opt){
    case 1:
        generaProductos alm = new generaProductos();
        alm.generaProductos();

When I execute my code, I always receive this:

Botas Futbol Hombre Marron S 16.99

Botas Futbol Hombre Marron S 16.99

Botas Futbol Hombre Marron S 16.99

(In English it would be Football boots men brown size S 16.99)

Answer 1

You cast a floating point value between 0 and 1 (exclusive) to int, which results in 0, and then multiply 0 by 3, which is still 0.

change

(int) Math.random() * 3

to

(int) (Math.random() * 3)

Answer 2

num = (int) Math.random() * 3;

will always be 0, because of order of precedence.

Math.random() is always < 1 so casting it to int will give you 0, then you multiply, still getting 0.