CODEWITHSUNDEEP
javaarraysreturn
vabasda
vabasda

Reputation: 5

Randomly take an int element from an integer array

I have an Integer array and I want to randomly take an element from those who are not null. I have tried this but after the else, I cannot use return because the method is int. But I don't know what to write after else in order to return at the beginning and take a new random element.

public int getRandomPosition(){
    Random x = new Random();
    int b = x.nextInt(2*number0fCardPairs);
    if (myArray[b] != null){
       return b;
    }
    else{
        return;
    }
}

Upvotes: 0

Views: 94

Answers (3)

XYZ
XYZ

Reputation: 83

You can achieve this by using a loop.

public int getRandomPosition(){
    Random random = new Random();
    int randomIdx = random.nextInt(array.length);

    // while array at randomIdx is null, continue getting new randomIdx
    while (array[randomIdx] == null) {
        randomIdx = random.nextInt(array.length);
    }

    return randomIdx;
}

Note that if all the elements inside the array are null, it will be an infinite loop. Hope you find this helpful!

Upvotes: 1

Daniel
Daniel

Reputation: 1460

You could make your method recursive:

private Random x = new Random();

public int getRandomPosition(){
    int b = x.nextInt(sizeOfArray);
    if (myArray[b] != null){
       return b;
    }
    // else {
    return getRandomPosition();
}

or using a while-loop

private Random x = new Random();

public int getRandomPosition(){
    Integer result = null; 
    do {
      int index = x.nextInt(sizeOfArray);
      result = myArray[index];
    } while (result == null);
    return result.intValue();
}

Theoretically, however, the method could run indefinitely if you're really unlucky. Therefore, it probably makes sense to include a counter, so for example only try max. 20 times, then return null:

private Random x = new Random();

public int getRandomPosition(){
    Integer result = null; 
    int tries = 0;
    do {
      int index = x.nextInt(sizeOfArray);
      result = myArray[index];
    } while (result == null && ++tries < 20);
    return result.intValue();
}

Upvotes: 1

Most Noble Rabbit
Most Noble Rabbit

Reputation: 2776

You can do:

Integer[] myArray = {1,2,3,null,5};

List<Integer> nonNullIntegers = Arrays.stream(myArray)
        .filter(Objects::nonNull)
        .collect(Collectors.toList());

Random random = new Random();
Integer randomInteger = nonNullIntegers.get(random.nextInt(nonNullIntegers.size()));

Upvotes: 0

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