added checksum calculation snippet

Author: Mcbencrafter

snippets/java/math/checksum.md

@@ -0,0 +1,24 @@
+---
+title: Checksum
+description: Calculates the checksum of an int
+author: Mcbencrafter
+tags: math,number,checksum
+---
+
+```java
+public static int checksum(int number) {
+    number = Math.abs(number);
+    int sum = 0;
+
+    while (number != 0) {
+        sum += number % 10;
+        number /= 10;
+    }
+
+    return sum;
+}
+
+// Usage:
+int number = 12345;
+System.out.println(checksum(number)); // 15 = 1+2+3+4+5
+```