How to generate Random numbers using SecureRandom

Question

I have the below code which uses java.util.Random , now I want to change to java.security.SecureRandom . How do I do the same operations with SecurRandom?

int rand = 0;
for (int i = 0; i < 8; i++) {
    rand = (int) (Math.random() * 3);
    switch (rand) {
        case 0:
            c = '0' + (int) (Math.random() * 10);
            break;
        case 1:
            c = 'a' + (int) (Math.random() * 26);
            break;
        case 2:
            c = 'A' + (int) (Math.random() * 26);
            break;
    }
}

Answer 1

SecureRandom random = SecureRandom.getInstance("SHA1PRNG");
int rand = 0;

for (int i = 0; i < 8; i++) {
    rand = random.nextInt(3);
    switch (rand) {
    case 0:
        c = '0' + random.nextInt(10);
        break;
    case 1:
        c = 'a' + random.nextInt(26);
        break;
    case 2:
        c = 'A' + random.nextInt(26);
        break;
    }

Answer 2

secureRandomObject.nextDouble() is essentially equivalent to Math.random()

So following code will work...

SecureRandom secureRandom = new SecureRandom();
int rand = 0;
for (int i = 0; i < 8; i++) {
    rand = (int) (secureRandom.nextDouble() * 3);
    switch (rand) {
        case 0:
            c = '0' + (int) (secureRandom.nextDouble() * 10);
            break;
        case 1:
            c = 'a' + (int) (secureRandom.nextDouble() * 26);
            break;
        case 2:
            c = 'A' + (int) (secureRandom.nextDouble() * 26);
            break;
    }
}

Answer 3

Do you wish to achieve something like this :

    int rand=0,c=0;;
SecureRandom secrnd=new SecureRandom();
for (int i = 0; i < 8; i++) {
    rand = (int) (secrnd.nextInt(10)% 3);
    switch (rand) {
    case 0:
        c = '0' + (int) (secrnd.nextInt(10) % 10);
        break;
    case 1:
        c = 'a' + (int) (secrnd.nextInt(10) % 26);
        break;
    case 2:
        c = 'A' + (int) (secrnd.nextInt(10) % 26);
        break;
    }

    System.out.println(c);
}

Please clarify your question , so that i can understand what you want to achieve with the above code.