如何获取第一个非空数组元素的索引？

Question

Is there any nice way to get the index of the first not null String array element? Yes, you can write

int index;
for (int i = 0; i < arr.length; i++) {
   if (arr[i] != null) {
       index = i;
       break;
   }
}

but maybe there is possible to do it in a more beautiful manner? For example, you can use ObjectUtils.firstNonNull method to get the first not null element of the array, maybe there's something similar to obtain index?

Answer 1

One trick is to create a stream of indexes, and then find the first one that points to a non-null value:

int index =
    IntStream.range(0, arr.length)
             .filter(i -> arr[i] != null)
             .findFirst()
             .orElse(-1 /* Or some other default */);

Answer 2

If you are using Java 9 there is a method called takeWhile() . you can use it in your array of numbers like so.

long index = Arrays.stream(yourArray).takeWhile(Objects::isNull).count();

Edit

In case there are no non-null elements index will be equal to the length of the array.

You can make a check for it.

if(index == array.length) {
    index = -1;
}

Answer 3

For example, like that in Java version earlier than 8:

static final Object ANY_NOT_NULL = new Object()
{
    @Override
    public boolean equals(final Object obj)
    {
        return obj != null;
    }
};

public static int firstIndexOfNotNull(Object... values)
{
    return Arrays.asList(values).indexOf(ANY_NOT_NULL);
}

Answer 4

Object[] dizi = { 1, 2, 3, 4, 5, 6, null, 8, 9, 10 };

    Object t = null;
    int len = dizi.length;
    System.out.println(IntStream.range(0, len).filter(i -> t == dizi[i]).findFirst().orElse(-1)); // can't find.);