java math.sqrt from array element

I've got two problems. Please find my code attached below:

public class Numbers {

    public static void main(String[] args) {
        double[] tab = { 9.0, 27, 5, 77 };
        System.out.println("array size: " + tab.length);

        for (int y = 0; y < tab.length; y++) {
            System.out.printf("%d", (int) tab[y]);
            System.out.print("    ");
            System.out.print(Math.sqrt(y));
            System.out.println();
        }

        // for(double i:tab){
        // System.out.println(tab[(int) i]);
        // }

    }
}

And now

1) my first problem is that I have some numbers in my array tab and then in the FOR loop I want to display in each line the element and its square root. But for the first element i get 0.0 as a square root. why? The other results are wrong as well to me.

my outcome:

array size: 4
9    0.0
27    1.0
5    1.4142135623730951
77    1.7320508075688772

2) second problem is with my for each loop which is commented. But when you uncomment it the it doesnt work because I get an error. The output:

array size: 4
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 9

What did I do wrong with this for each loop? Why eclipse shows that I ask about 9-th element?

Thank you for help in advance - all answers are appreciated :)