MountainHandler.java is CREATED and DONE

src/main/java/model/elements/MountainHandler.java

+package model.elements;
+
+import model.ModelElement;
+import model.Mountain;
+import util.Position;
+
+import java.util.*;
+
+public class MountainHandler implements ElementHandler {
+    private final List<Mountain> mountains;
+
+    public MountainHandler(List<Mountain> mountains) {
+        this.mountains = mountains;
+    }
+
+    @Override
+    public void addElement(Position position) {
+        mountains.add(new Mountain(position));
+    }
+
+    @Override
+    public void removeElement(Position position) {
+        mountains.removeIf(mountain -> mountain.getPosition().equals(position));
+    }
+
+    @Override
+    public boolean hasElement(Position position) {
+        return mountains.stream().anyMatch(mountain -> mountain.getPosition().equals(position));
+    }
+
+
+    @Override
+    public ModelElement getModelElement() {
+        return ModelElement.MOUNTAIN;
+    }
+}