Eventually java.lang.Arrayindexoutofboundsexception occurs

Question

I made a simple algorithm of a book and there are two possible results. To test these results I have to run the program several times until Math.Random() generates the possible numbers and displays the two possible results. The strange thing was that when I was running the code there came a point where he presented a message

"Exception in thread "main" java.lang.Arrayindexoutofboundsexception: 3 at matrizReferencia3.Hobbits.main(Hobbits.java:25)"

But if I run the program again it returns to present a result. I’d like to understand why this message appears, if it’s something dangerous I’m doing in my code.

package matrizReferencia3;

public class Hobbits {
String name;

public static void main(String[] args) {

    Hobbits[] h = new Hobbits[3];
    int z = 0;
    int posicao = 5;

    while(z < 3){ 
        h[z] = new Hobbits();
        z++;
    }

    while (posicao > 3){
    posicao =(int) (Math.random() *10);
    }

    if (posicao == 2){
        h[posicao].name = "sam";
    }
    else{
        h[posicao].name = "frodo";
    }
    System.out.print(h[posicao].name + " is a ");
    System.out.println("good Hobbit name");
}
}

Answer 1

The error indicates that you are trying to access an array item h whose index is greater than the size of that array.

The array has been set to have 3 items:

Hobbits[] h = new Hobbits[3];

Items will have as index the values 0 for the first, 1 for the second and 2 for the third.
In the code part, where a random index is generated, it is allowed that the value 3 is generated:

while (posicao > 3){
    posicao =(int) (Math.random() *10);
}

So that this does not happen make the value is not greater than 2:

while (posicao > 2){
    posicao =(int) (Math.random() *10);
}