Shuffle sort - Fisher Yates, why cant I find random number between 0 and N-1?

While studying Shuffle sort, I learnt Fisher Yates solution. It loops for 0 to array length and finds a random number between 0(inclusive) and the loop index (inclusive) and NOT 0 and N-1. Finding a random number between 0 and N-1 does not give a random solution. But I couldn't find the reason for the same.

public static void sort(Comparable[] a){

    for(int i = 0 ; i < a.length ; i++){ 

        int r = StdRandom.uniform(i+1); 
        // why cant this be a.length-1

        exch(a, i, r);

    }

}