How to get elements of an array that is not null

Question

I am doing gift (String-type) storage, using arrays, with the maximum 500 million. I want to get the number of used elements in an array like how many gifts are currently in sto

Answer 1

You can iterate through the array and count the initialized array elements.

int counter = 0;
for (int i = 0; i < arrayName.length; i ++)
    if (arrayName[i] != null)
        counter ++;

Also it would be even better if you used ArrayList<String> so you could use size()

ArrayList<String> arrayName = new ArrayList<String>(20);
System.out.println(arrayName.size());

It will print 0, as there are no elements added to the ArrayList.

Answer 2

You can use Arrays.stream to iterate over this array of strings, then use filter to select nonNull elements and count them:

String[] arr = {"aaa", null, "bbb", null, "ccc", null};

long count = Arrays.stream(arr).filter(Objects::nonNull).count();

System.out.println(count); // 3

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Or if you want to find the index of the first null element to insert some value there:

int index = IntStream.range(0, arr.length)
        .filter(i -> arr[i] == null)
        .findFirst()
        .getAsInt();

arr[index] = "ffffd";

System.out.println(index); // 1
System.out.println(Arrays.toString(arr));
// [aaa, ffffd, bbb, null, ccc, null]

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^{See also: How to find duplicate elements in array in effective way?}