implement solution

Author: SteffenLm

CoordinateComparator.java

@@ -1,5 +1,6 @@
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.Comparator;
 
 public class Exercise {
 
@@ -12,6 +13,13 @@ public static void main(String[] args) {
     coordinates.add(new Coordinate(6, 8));
     coordinates.add(new Coordinate(1, 9));
 
+    class CoordinateComparator implements Comparator<Coordinate> {
+      @Override
+      public int compare(Coordinate c1, Coordinate c2) {
+        return Integer.valueOf(c1.getX()).compareTo(c2.getX());
+      }
+    }
+
     Collections.sort(coordinates, new CoordinateComparator());
 
     for (Coordinate c : coordinates) {