Merge pull request #906 from FridaTveit/RobotSimulatorGridPositionEquals

robot-simulator: improve equals for GridPosition

exercises/robot-simulator/src/main/java/GridPosition.java

         this.y = y;
     }
 
-    /*
-     * This equals method is of deliberately narrow scope (only allows comparison with another GridPosition) to increase
-     * readability. In general, one should provide a full implementation of Object.equals(Object obj) and a
-     * corresponding implementation of Object.hashCode(). See
-     *
-     * https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html#equals(java.lang.Object)
-     *
-     * and
-     *
-     * https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html#hashCode()
-     *
-     * for more information.
-     */
-    boolean equals(final GridPosition gridPosition) {
-        return this.x == gridPosition.x && this.y == gridPosition.y;
+    @Override
+    public int hashCode() {
+        final int prime = 31;
+        int result = 1;
+        result = prime * result + x;
+        result = prime * result + y;
+        return result;
     }
 
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        } else if (obj == null || getClass() != obj.getClass()) {
+            return false;
+        } else if (x != ((GridPosition) obj).x || y != ((GridPosition)obj).y) {
+            return false;
+        } else {
+            return true;
+        }
+    }
 }