Input validation for java nCr

java/calculators/ncr.java

@@ -1,7 +1,10 @@
 package calculators;
+import java.util.InputMismatchException;
 import java.util.Scanner;
 
 class CombinationCalculator {
+	private static Scanner scanner = new Scanner(System.in);
+
 	private static int factorial(int n) {
 		int res = 1;
 
@@ -16,19 +19,28 @@ class CombinationCalculator {
 		return factorial(n) / (factorial(r) * factorial(n - r));
 	}
 
+	private static int intInput(String message) {
+		int value = -1;
+
+		while (value < 0) {
+			try {
+				System.out.print(message);
+				value = scanner.nextInt();
+			} catch (InputMismatchException e) {
+				scanner.next();
+			}
+		}
+
+		return value;
+	}
+
 	public static void main(String[] args) {
-		// Open a scanner and take the relevant inputs
+		// Take inputs
-		Scanner scan = new Scanner(System.in);
+		int n = intInput("Please input the value for n: ");
-
+		int r = intInput("Please input the value for r: ");
-		System.out.print("Please input the value for n: ");
+		scanner.close();
-		int n = scan.nextInt();
-
-		System.out.print("Please input the value for r: ");
-		int r = scan.nextInt();
-
-		// Close the scanner, and calculate the result
-		scan.close();
 
+		// Calculate the result
 		int result = nCr(n, r);
 		System.out.println(result);
 	}