Create factorial calculation method

src/main/java/Calculations.java

@@ -2,4 +2,18 @@ public class Calculations {
     public int calculateSquare(int num) {
         return (num * num);
     }
+
+    public int calculateFactorial(int num) {
+        if (num < 0) {
+            throw new IllegalArgumentException("Factorial is not defined for negative numbers");
+        }
+        if (num == 0 || num == 1) {
+            return 1; // Factorial of 0 and 1 is 1
+        }
+        int factorial = 1;
+        for (int i = 2; i <= num; i++) {
+            factorial *= i;
+        }
+        return factorial;
+    }
 }