Implementation of 2D mode

app/src/main/java/chess/model/Model2D.java

@@ -0,0 +1,15 @@
+package chess.model;
+
+import java.util.Observable;
+
+public class Model2D extends Observable {
+    public int x;
+    public int y;
+
+    public void set(int i, int j){
+        this.x = i;
+        this.y = j;
+        setChanged();
+        notifyObservers();
+    }
+}