Added 20 solutions

Java/BigNumber/Java BigInteger/Solution.java

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+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
+import java.util.Scanner;
+import java.math.BigInteger;
+
+public class Solution {
+    public static void main(String[] args) {
+        Scanner scan = new Scanner(System.in);
+        BigInteger a = new BigInteger(scan.next());
+        BigInteger b = new BigInteger(scan.next());
+        System.out.println(a.add(b));
+        System.out.println(a.multiply(b));
+    }
+}