September Morn Update

Task/Factorial/Java/factorial-2.java

@@ -1,7 +1,56 @@
-public static long fact(final int n) {
-    if (n < 0){
-        System.err.println("No negative numbers");
-        return 0;
+package programas;
+
+import java.math.BigInteger;
+import java.util.InputMismatchException;
+import java.util.Scanner;
+
+public class RecursiveFactorial {
+
+  public BigInteger factorial(BigInteger n) {
+    if ( n == null ) {
+      throw new IllegalArgumentException();
     }
-    return (n < 2) ? 1 : n * fact(n - 1);
+
+    else if ( n.equals(BigInteger.ZERO) ) {
+      return BigInteger.ONE;
+    }
+    else if ( n.signum() == - 1 ) {
+      // negative
+      throw new IllegalArgumentException("Argument must be a non-negative integer");
+    }
+    else {
+      return n.equals(BigInteger.ONE)
+          ? BigInteger.ONE
+          : factorial(n.subtract(BigInteger.ONE)).multiply(n);
+    }
+  }
+
+  public static void main(String[] args) {
+    Scanner scanner = new Scanner(System.in);
+    BigInteger number, result;
+    boolean error = false;
+    System.out.println("FACTORIAL OF A NUMBER");
+    do {
+      System.out.println("Enter a number:");
+      try {
+        number = scanner.nextBigInteger();
+        result = new RecursiveFactorial().factorial(number);
+        error = false;
+        System.out.println("Factorial of " + number + ": " + result);
+      }
+      catch ( InputMismatchException e ) {
+        error = true;
+        scanner.nextLine();
+      }
+
+      catch ( IllegalArgumentException e ) {
+        error = true;
+        scanner.nextLine();
+      }
+    }
+    while ( error );
+    scanner.close();
+
+  }
+
 }