CODEWITHSUNDEEP
javarandom
Basant Singh
Basant Singh

Reputation: 5916

Pick a number randomly from two numbers

I have two integers, let them be

int a = 35:
int b = 70;

I want to pick one of them randomly at runtime and assign to another variable. I.e.

int c = a or b:

One of the ways that come into my mind is to create an array with these two integers and find a random integer between 0 and 1 and use it as the index of the array to get the number..

Or randomize boolean and use it in if-else.

My question is that is there a better and more efficient way to achieve this? I.e. pick a number from two previously defined integers?

Upvotes: 9

Views: 16159

Answers (6)

Rocky
Rocky

Reputation: 19

int a=1;
int b=2;
int get = new Random().nextBoolean()? a : b;

Upvotes: 0

Andreas Troelsen
Andreas Troelsen

Reputation: 479

Is there a specific reason you are asking for a more efficient solution? Unless this functionality sits in a very tight inner loop somewhere (e.g. in a ray tracer), you might be trying to prematurely optimize your code.

If you would like to avoid the array, and if you don't like the "bloat" of an if-statement, you can use the ternary choice operator to pick between the two:

int a = 35;
int b = 70;
int c = random.nextBoolean() ? a : b;

where random is an instance of java.util.Random. You can store this instance as a final static field in your class to reuse it.

If you don't require true randomness, but just want to switch between the two numbers in each invocation of the given block of code, you can get away with just storing a boolean and toggling it:

...
int c = toggle ? a : b;
toggle = !toggle;

Since I can't comment on other answers, I'd like to point out an issue with some of the other answers that suggest generating a random integer in a bigger range and making a decision based on whether the result is odd or even, or if it's lower or greater than the middle value. This is in effect the exact same thing as generating a random integer between 0 and 1, except overly complicated. The nextInt(n) method uses the modulo operator on a randomly generated integer between -2^31 and (2^31)-1, which is essentially what you will be doing in the end anyway, just with n = 2.

If you are using the standard library methods like Collections.shuffle(), you will again be overcomplicating things, because the standard library uses the random number generator of the standard library.

Note that all of the suggestions (so far) are less efficient than my simple nextBoolean() suggestion, because they require unnecessary method calls and arithmetic.

Upvotes: 9

Nithin CV
Nithin CV

Reputation: 1136

You can simply use secure random generator(java.security.SecureRandom ). 

try {
    r = SecureRandom.getInstance("SHA1PRNG");
    boolean b1 = r.nextBoolean(); 

    if (b1) {
        c = a;
    } else {
        c = b;
    }
} catch (NoSuchAlgorithmException nsae) {
    // Process the exception in some way or the other
}

Refer this link for more information

Upvotes: 1

Baby
Baby

Reputation: 5092

Another way to do this is, store the numbers into a list, shuffle, and take the first element.

ArrayList<Integer> numbers=new ArrayList<Integer>();
numbers.add(35);
numbers.add(70);
Collections.shuffle(numbers);

numbers.get(0);

Upvotes: 6

kiDDevil
kiDDevil

Reputation: 23

Randomize an integer between 1 and 10, if it's more than 5 then take the value of b other wise go with a. As far as I know there are no other ways to select from integers.

Upvotes: 0

akshay2000
akshay2000

Reputation: 824

In my opinion, main problem here is entropy for two numbers rather than making use of that entropy. Indexed array or boolean are essentially the same thing. What else you can do (and, hopefully, it will be more random) is to make Java give you a random number between limits say 0 to 100. Now, if the chosen random number is odd, you pick int c = a. Pick b otherwise. I could be wrong, but picking random between 0 to 100 seems more random as compared to picking random between two numbers.

Upvotes: 1

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