java中关于copyEven的问题

Question

The question is as follows:

Write a Java method int[] copyEven(int[] nums) that copy elements at even indices to a new array.

It must return the new array of the correct length with those elements inside.

For example

copyEven([1, 2, 3]) → [1, 3]
copyEven([1, 2, 3, 4]) → [1, 3]

Below is my code:

public static int [] copyEven(int[] nums){
    int n =nums.length;
    int a=0;
    for (int i=0;i<n;i++){
        if (nums[i]%2 !=0){
            a++;
    }
    int c=a;
    int [] arr=new int[c];
    int b=0;
    for (int j=0;b<a;j++){
        if (nums[j]%2 !=0){
            arr[b]=nums[j];
            b++;}
        }
    }
    return arr;
}

I am just a beginner on code, and this is my first time using this website. I searched online and found that in similar questions, the number of odd numbers is provided. Thus, I plan to use a in the code to count the number of odd numbers at first, then create a new array to finish the question. However, NetBeans told me that in int [] arr=new int[c] ,the array is written to,never read from. I do not understand what that means. I would appreciate it very much if you can help me, thank you!

Answer 1

Here you can get all elements at even indices.
Indexing started from 1 as your given examples said.

public static int[] copyEven(int[] nums) {
    int length = nums.length;
    int numberOfEvenNumbers = (length % 2 == 0) ? length / 2 : length / 2 + 1;

    int[] copy = new int[numberOfEvenNumbers];
    int index = 0;

    for (int i = 0; i < nums.length; i += 2) {
        copy[index] = nums[i];
        index++;
    }
    return copy;
}