如何在java中找到数组的索引

Question

i am trying to use this function but it is giving that index is -1. so what can i do

int[] veer = {14,25,14,56,15,36,56,77,18,29,49};

int a = Arrays.asList(veer).indexOf(14);

System.out.println("my array at position 14 is :" + (a));

Answer 1

I assume, you want to learn/test what indexOf is doing. The problem is, that Arrays.asList(veer) returns list containing one element - whole array.

When I split the code to multiple lines, it is doing:

    int[] orig = {14,25,14,56,15,36,56,77,18,29,49};
    List<int[]> origList = Arrays.asList(orig);

and that's why, your indexOf is not able to find 14 in a list, because simply said, there is no integer in list.

When you use wrapper type, it works as you might expect

    Integer[] veer = {14,25,14,56,15,36,56,77,18,29,49};
    List<Integer> list = Arrays.asList(veer);
    int a = list.indexOf(25); // I changed to 25
    System.out.println("my array at position 25 is :" + a);

which prints index 1.

To learn about wrapping/unwrapping array, you can read more here Converting Array of Primitives to Array of Containers in Java but changing int[] to Integer[] is simplest in this case (you are not forced by API to accept int[] ).

Answer 2

In your code

int[] veer = {14,25,14,56,15,36,56,77,18,29,49};

to

Integer[] veer = {14,25,14,56,15,36,56,77,18,29,49};

because indexOf expect a object type since it is primitive it is return as -1(-1 represents not found)