The basic idea behind “isIn” is to inspect an array to see if it contains a given string.

So, in this write-up, we will explore different ways of implementing the “isIn” method in Java.

isIn Java Implementation

Typically, we need to create a static method with two parameters: an array and a given string.

The method should return a boolean value denoting whether the passed string is present in the array.

Using Stream API

Let’s see how we can use the Stream API to achieve our objective:

        public static boolean isInUsingStreamApi(String[] array, String value) {
            if (array == null || value == null) {
                return false;

            Optional<String> searchedElement =
                    .filter(element -> element != null && element.equals(value))
            return searchedElement.isPresent();

To keep things simple, we will not repeat the first condition for the remaining implementations.

Using For-each Loop

Next, we will use a for-each loop to iterate through the array. Then, we will check whether each element is equal to the target.

Here’s an example implementation:

        public static boolean isInUsingForLoop(String[] array, String value) {
            for (String str : array) {
                if (str != null && str.equals(value)) {
                    return true;
            return false;

As we can see, we used the equals() method to test if the specified string is in the array.

Using Arrays.binarySearch()

Similarly, we can implement the isIn method using Arrays.binarySearch():

        public static boolean isInUsingBinarySearch(String[] array, String value) {
            int result = Arrays.binarySearch(array, value);
            return result >= 0;

Please note that binarySearch() searches for the passed value using the binary search algorithm.

Using Arrays.asList

Alternatively, we can use Arrays.asList() to check whether a string is among the elements:

        public static boolean isInUsingArrays(String[] array, String value) {
            return Arrays.asList(array)

As shown above, we called contains() which returns true if the searched value exists in the array. Otherwise, false.

Using HashSet

HashSet provides another way to accomplish the same thing:

        public static boolean isInUsingHashSet(String[] array, String value) {
            Set<String> setSet = new HashSet<>(Arrays.asList(array));
            return setSet.contains(value);


In this short article, we demonstrated using practical examples how to implement isIn in Java.