Add SlidingWindowExample class for max sum subarray

src/test/java/com/thealgorithms/slidingwindow/Maximum Sum Subarray of Size K

@@ -0,0 +1,26 @@
+public class SlidingWindowExample {
+    public static int maxSumSubarray(int[] arr, int k) {
+        int maxSum = 0;
+        int windowSum = 0;
+
+        // Compute sum of first window
+        for (int i = 0; i < k; i++) {
+            windowSum += arr[i];
+        }
+        maxSum = windowSum;
+
+        // Slide the window
+        for (int i = k; i < arr.length; i++) {
+            windowSum += arr[i] - arr[i - k];  // Add next element, remove first of the previous window
+            maxSum = Math.max(maxSum, windowSum);
+        }
+
+        return maxSum;
+    }
+
+    public static void main(String[] args) {
+        int[] arr = {2, 1, 5, 1, 3, 2};
+        int k = 3;
+        System.out.println("Maximum sum of subarray of size " + k + " is: " + maxSumSubarray(arr, k));
+    }
+}