Function to generate an array of random numbers with no repetitions

I'm creating a function to generate an arry of random and not repeating numbers.What am i doing wrong?

With this code the function fills the array repeating some numbers.

for(int i=0;i<n;i++)
        {
          numero = random.nextInt(delta) + da;
          for(int j=0;j<n;j++)
          {
            if(numero==estratti[j])
            {
              numero = random.nextInt(delta) + da;
              j=0;
            }        
          }
          estratti[i] = numero;
        }