findArrayDifference()

Step 1: Define the Method

First, we need to define our function that accepts two integer arrays as parameters. We name this function findArrayDifference.

public static int[] findArrayDifference(int[] array1, int[] array2) {
    // Function Implementation
}

Step 2: Instantiate a HashSet

Next, we create a HashSet instance to store the unique numbers from the second array. HashSet is a Java collection that stores unique elements and allows efficient contains operations.

HashSet<Integer> set = new HashSet<>();
for (int num : array2) {
    set.add(num);
}

Step 3: Determining Differences

We then iterate over the first array and for each number, we check if it exists in the HashSet. If it doesn't, this means that this number is exclusively present in the first array, it's part our array difference.

List<Integer> difference = new ArrayList<>();
for (int num : array1) {
    if (!set.contains(num)) {
        difference.add(num);
    }
}

Step 4: Convert the Result to an Array

The final result needs to be an integer array. We can convert our result list back into an array using toArray method.

Integer[] result = difference.toArray(new Integer[0]);

Conclusion & Full Code

Finally, our findArrayDifference function first fills up a Set with elements from the second array, checks for each element in the first array if it exists in the Set or not. If not, it appends it to our result list. And then, it converts this list into an array and returns it.

public static int[] findArrayDifference(int[] array1, int[] array2) {
    HashSet<Integer> set = new HashSet<>();
    for (int num : array2) {
        set.add(num);
    }

    List<Integer> difference = new ArrayList<>();
    for (int num : array1) {
        if (!set.contains(num)) {
            difference.add(num);
        }
    }

    int[] result = new int[difference.size()];
    for (int i = 0; i < difference.size(); i++) {
        result[i] = difference.get(i);
    }
    return result;
}