findMedianArray()

Step 1: Sort the Array

In order to find the median of an array, it is necessary to have access to the middle elements. The easiest way to accomplish this is by first sorting the array. In Java, this can be done simply by using the Arrays.sort method.

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        int[] nums = {5, 2, 8, 9, 1};
        Arrays.sort(nums);
    }
}

Step 2: Identify the Middle

The median of an array is the middle number if the array's size is odd or the average of the two middle numbers if the size is even. Therefore, we need to check the size of the sorted array and find the middle index or indices.

int middle = nums.length / 2;

Step 3: Find the Median

With the middle index, you can now locate the median. If the number of elements is odd, then the median is simply the middle element. If it is even, then the median will be calculated as the average of the middle two elements.

double median;
if (nums.length % 2 == 0) {
    median = (nums[middle-1] + nums[middle]) / 2.0;
}
else {
    median = nums[middle];
}

Step 4: Wrap in a Function

To make this code reusable, it can be wrapped in a function which takes an array as input and returns the median.

public double findMedian(int[] nums) {
    Arrays.sort(nums);
    int middle = nums.length / 2;
    if (nums.length % 2 == 0) {
        return (nums[middle-1] + nums[middle]) / 2.0;
    } else {
        return nums[middle];
    }
}

Step 5: Test Your Function

Finally, you should test your function to ensure it behaves as expected. This could be done by feeding it various arrays and checking the results.

public class Main {
    public static void main(String[] args) {
        Main main = new Main();
        System.out.println(main.findMedian(new int[]{5, 2, 8, 9, 1}));  // should print 5.0
        System.out.println(main.findMedian(new int[]{5, 2, 8, 9, 1, 6})); // should print 5.5
    }
}

This concludes the step-by-step guide to create a findMedian function in Java which sorts an array and finds the median value.