diff --git a/src/berack96/sim/util/graph/Edge.java b/src/berack96/sim/util/graph/Edge.java
index d002cef..c8f1965 100644
--- a/src/berack96/sim/util/graph/Edge.java
+++ b/src/berack96/sim/util/graph/Edge.java
@@ -27,7 +27,7 @@ public class Edge<V, W extends Number> {
      *
      * @param source      the source of the edge
      * @param destination the destination of the edge
-     * @param weight      the weight od the edge
+     * @param weight      the weight of the edge
      */
     public Edge(V source, V destination, W weight) {
         this.source = source;
diff --git a/src/berack96/sim/util/graph/Graph.java b/src/berack96/sim/util/graph/Graph.java
index 63a141f..98d285a 100644
--- a/src/berack96/sim/util/graph/Graph.java
+++ b/src/berack96/sim/util/graph/Graph.java
@@ -4,6 +4,7 @@ import java.io.FileReader;
 import java.io.FileWriter;
 import java.io.IOException;
 import java.util.Collection;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.function.Consumer;
@@ -24,11 +25,12 @@ import berack96.sim.util.graph.visit.VisitStrategy;
  */
 public interface Graph<V, W extends Number> extends Iterable<V> {
 
-    String NOT_DAG = "The graph is not a DAG";
-    String NOT_CONNECTED = "The source vertex doesn't have a path that reach the destination";
-    String PARAM_NULL = "The parameter must not be null";
-    String VERTEX_NOT_CONTAINED = "The vertex must be contained in the graph";
-
+    final String NOT_DAG = "The graph is not a DAG";
+    final String NOT_CONNECTED = "The source vertex doesn't have a path that reach the destination";
+    final String PARAM_NULL = "The parameter must not be null";
+    final String VERTEX_NOT_CONTAINED = "The vertex must be contained in the graph";
+    final Gson GSON = new Gson();
+    
     /**
      * Tells if the graph has some cycle.<br>
      * A cycle is detected if visiting the graph G starting from V1 (that is any of the vertex of G),
@@ -515,7 +517,7 @@ public interface Graph<V, W extends Number> extends Iterable<V> {
     /**
      * Get a sub-graph of the current one with only the vertex marked with the selected markers.<br>
      * Each vertex will have all his edges, but only the ones with the destination marked with the same marker.<br>
-     * If the marker is null then the returning graph will have all the vertices that are not marked by any marker.<br>
+     * If the marker is not specified or is null then the returning graph will have all the vertices that are not marked by any marker.<br>
      * If the graph doesn't contain any vertex with that marker then an empty graph is returned.
      *
      * @param marker one or more markers
@@ -547,19 +549,21 @@ public interface Graph<V, W extends Number> extends Iterable<V> {
     Map<V, List<Edge<V, W>>> distance(V source) throws NullPointerException, IllegalArgumentException;
 
     static void save(Graph<?, ?> graph, String file) throws IOException {
-    	GraphSaveStructure<?, ?> save = new GraphSaveStructure<>(graph);
-    	Gson gson = new Gson();
+    	save(graph, "", file);
+    }
+    
+    static <V, W extends Number> void save(Graph<V, W> graph, String other, String file) throws IOException {
+    	GraphSaveStructure<V, W> save = new GraphSaveStructure<>(graph, other);
     	FileWriter writer = new FileWriter(file);
     	
-    	writer.write(gson.toJson(save));
+    	GSON.toJson(save, writer);
     	writer.close();
     }
     
     @SuppressWarnings("unchecked")
-    static <V, W extends Number> void load(Graph<V, W> graph, String file) throws IOException {
+    static <V, W extends Number> String load(Graph<V, W> graph, String file, Class<V> classV, Class<W> classW) throws IOException {
     	graph.removeAllVertex();
     	
-    	Gson gson = new Gson();
     	FileReader reader = new FileReader(file);
     	StringBuilder fileContent = new StringBuilder();
     	int c;
@@ -567,21 +571,53 @@ public interface Graph<V, W extends Number> extends Iterable<V> {
     	while((c = reader.read()) != -1)
     		fileContent.append((char)c);
     	reader.close();
-    	GraphSaveStructure<V, W> save = gson.fromJson(fileContent.toString(), GraphSaveStructure.class);
+    	GraphSaveStructure<V, W> save = GSON.fromJson(fileContent.toString(), GraphSaveStructure.class);
     	
-		graph.addAllVertices(save.vertices);
-    	graph.addAllEdges(save.edges);
+    	for(String str : save.vertices)
+    		graph.addVertex(GSON.fromJson(str, classV));
+    	
+    	for(int i = 0; i<save.edges.src.size(); i++) {    	
+    		V s = GSON.fromJson(save.edges.src.get(i), classV);
+    		V d = GSON.fromJson(save.edges.dest.get(i), classV);
+    		W w = GSON.fromJson(save.edges.weight.get(i), classW);
+    		graph.addEdge(s, d, w);
+    	}
+    	return save.other;
     }
     
     class GraphSaveStructure<V, W extends Number> {
     	public GraphSaveStructure() {}
-    	protected GraphSaveStructure(Graph<V, W> graph) {
-    		vertices = graph.vertices();
-    		edges = graph.edges();
+    	protected GraphSaveStructure(Graph<V, W> graph, String other) {
+    		vertices = new LinkedList<>();
+    		
+    		for(V v: graph.vertices())
+    			vertices.add(GSON.toJson(v));
+			edges = new EdgeSaveStructure<>(graph.edges());
+    		this.other = other;
     	}
     	
-    	public Collection<V> vertices;
-    	public Collection<Edge<V, W>> edges;
+    	public List<String> vertices;
+    	public EdgeSaveStructure<V, W> edges;
+    	public String other;
+    }
+    
+    class EdgeSaveStructure<V, W extends Number> {
+    	public EdgeSaveStructure() {}
+    	protected EdgeSaveStructure(Collection<Edge<V, W>> edges) {
+    		src = new LinkedList<>();
+    		dest = new LinkedList<>();
+    		weight = new LinkedList<>();
+    		
+    		for(Edge<V, W> ed : edges) {
+    			src.add(GSON.toJson(ed.getSource()));
+    			dest.add(GSON.toJson(ed.getDestination()));
+    			weight.add(GSON.toJson(ed.getWeight()));
+    		}
+    	}
+
+    	public List<String> src;
+    	public List<String> dest;
+    	public List<String> weight;
     }
     
     // TODO maybe -> STATIC saveOnFile(orString) INSTANCE loadFromFile(orString), but need JSON parser
diff --git a/src/berack96/sim/util/graph/MapGraph.java b/src/berack96/sim/util/graph/MapGraph.java
index 1cd47d1..ae0fa6d 100644
--- a/src/berack96/sim/util/graph/MapGraph.java
+++ b/src/berack96/sim/util/graph/MapGraph.java
@@ -416,17 +416,18 @@ public class MapGraph<V, W extends Number> implements Graph<V, W> {
         final Graph<V, W> sub = new MapGraph<>();
         final Set<V> allVertices = new HashSet<>();
         final Set<Object> allMarkers = new HashSet<>();
+        final boolean isEmpty = (marker == null || marker.length == 0);
         
-        if (marker != null)
+        if (!isEmpty)
         	for (Object mark: marker)
         		allMarkers.add(mark);
 
         markers.forEach( (mark, set) -> {
-        	if (marker == null || allMarkers.contains(mark))
+        	if (isEmpty || allMarkers.contains(mark))
         		allVertices.addAll(set);
         });
-        
-        if (marker == null) {
+
+        if (isEmpty) {
             Collection<V> toAdd = vertices();
             toAdd.removeAll(allVertices);
             allVertices.clear();
diff --git a/src/berack96/sim/util/graph/view/GraphInfo.java b/src/berack96/sim/util/graph/view/GraphInfo.java
index e6e2530..f599f5e 100644
--- a/src/berack96/sim/util/graph/view/GraphInfo.java
+++ b/src/berack96/sim/util/graph/view/GraphInfo.java
@@ -4,8 +4,6 @@ import java.awt.Color;
 import java.awt.Component;
 import java.awt.GridLayout;
 import java.awt.event.ItemEvent;
-import java.io.File;
-import java.io.FileWriter;
 import java.io.IOException;
 import java.util.HashMap;
 import java.util.LinkedList;
@@ -22,8 +20,6 @@ import javax.swing.JPanel;
 import javax.swing.JTextField;
 import javax.swing.border.BevelBorder;
 
-import com.google.gson.Gson;
-
 import berack96.sim.util.graph.Graph;
 import berack96.sim.util.graph.view.edge.EdgeListener;
 import berack96.sim.util.graph.view.vertex.VertexListener;
@@ -141,24 +137,34 @@ public class GraphInfo<V, W extends Number> extends JPanel {
         components.forEach(panelVertex::add);
         components.clear();
 
+        /* SAVE/LOAD errors */
+        JLabel textResult = new JLabel();
+        textResult.setForeground(Color.RED);
+        
+        JPanel panelErrors = new JPanel();
+        panelErrors.setOpaque(false);
+        panelErrors.add(textResult);
+        
         /* SAVE/LOAD */
-        /*
         JTextField fileText = new JTextField();
         JButton saveB = new JButton("Save");
         saveB.addActionListener(a -> {
         	try {
-				Graph.save(graphPanel.getGraph(), fileText.getText());
+				graphPanel.save(fileText.getText());
+				textResult.setText("");
 			} catch (IOException e1) {
 				e1.printStackTrace();
+				textResult.setText(e1.getMessage());
 			}
         });
         JButton loadB = new JButton("Load");
         loadB.addActionListener(a -> {
         	try {
-        		Graph<V, W> graph = graphPanel.getGraph();
-				Graph.load((Graph<Object, Number>) graph, fileText.getText());
+				graphPanel.load(fileText.getText());
+				textResult.setText("");
 			} catch (IOException e1) {
 				e1.printStackTrace();
+				textResult.setText(e1.getMessage());
 			}
         });
         components.add(new JLabel("File to save/load: "));
@@ -172,7 +178,6 @@ public class GraphInfo<V, W extends Number> extends JPanel {
         panelSave.setLayout(new GridLayout(components.size()/2, 2, 2*2, 2*2));
         components.forEach(panelSave::add);
         components.clear();
-        */
 
         /* ADDING COMPONENTS */
         this.setBackground(Color.LIGHT_GRAY);
@@ -182,6 +187,8 @@ public class GraphInfo<V, W extends Number> extends JPanel {
         this.add(panelDescription);
         this.add(panelInfo);
         this.add(panelVertex);
+        this.add(panelErrors);
+        this.add(panelSave);
         /*this.add(panelSave);*/
 
         modVertex.doClick();
diff --git a/src/berack96/sim/util/graph/view/GraphPanel.java b/src/berack96/sim/util/graph/view/GraphPanel.java
index b547089..c15c7ee 100644
--- a/src/berack96/sim/util/graph/view/GraphPanel.java
+++ b/src/berack96/sim/util/graph/view/GraphPanel.java
@@ -1,21 +1,31 @@
 package berack96.sim.util.graph.view;
 
+import java.awt.Component;
+import java.awt.Container;
+import java.awt.Graphics;
+import java.awt.Graphics2D;
+import java.awt.Point;
+import java.awt.Rectangle;
+import java.awt.RenderingHints;
+import java.awt.event.KeyListener;
+import java.awt.event.MouseListener;
+import java.awt.event.MouseMotionListener;
+import java.io.IOException;
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Observer;
+import java.util.Set;
+
+import berack96.sim.util.graph.Edge;
 import berack96.sim.util.graph.Graph;
 import berack96.sim.util.graph.MapGraph;
 import berack96.sim.util.graph.Vertex;
 import berack96.sim.util.graph.view.edge.EdgeComponent;
 import berack96.sim.util.graph.view.vertex.VertexComponent;
 
-import java.awt.*;
-import java.awt.event.KeyListener;
-import java.awt.event.MouseListener;
-import java.awt.event.MouseMotionListener;
-import java.util.Collection;
-import java.util.HashSet;
-import java.util.Observer;
-import java.util.Set;
-
-@SuppressWarnings("unchecked")
+@SuppressWarnings({"unchecked", "deprecation"})
 public class GraphPanel<V, W extends Number> extends Component {
 
 	private static final long serialVersionUID = 1L;
@@ -60,8 +70,14 @@ public class GraphPanel<V, W extends Number> extends Component {
 
         if (component == null) {
             VertexComponent<V> v = new VertexComponent<>(new Vertex<>(graph, vertex));
-            if (!graph.contains(vertex)) {
-                v.vertex.addIfAbsent();
+            v.vertex.addIfAbsent();
+            boolean isContained = false;
+            
+            for(Component comp : vertices.getComponents())
+            	if (comp.equals(v))
+            		isContained = true;
+            
+            if (!isContained) {
                 v.setBounds(vertexRender.getBox(v, center));
                 vertices.add(v);
             }
@@ -81,6 +97,20 @@ public class GraphPanel<V, W extends Number> extends Component {
         vertex.setLocation(rectangle.x, rectangle.y);
     }
 
+    public void addEdge(Edge<V, W> edge) {
+    	VertexComponent<V> vSource = null;
+    	VertexComponent<V> vDest = null;
+    	for (Component comp : vertices.getComponents()) {
+    		VertexComponent<V> temp = (VertexComponent<V>) comp;
+    		V vTemp = temp.vertex.getValue();
+    		if (vSource == null && vTemp.equals(edge.getSource()))
+    			vSource = temp;
+    		if (vDest == null && vTemp.equals(edge.getDestination()))
+    			vDest = temp;
+    	}
+    	addEdge(vSource, vDest, edge.getWeight());
+    }
+    
     public void addEdge(VertexComponent<V> source, VertexComponent<V> dest, W weight) {
         try {
             Point center = new Point(Math.abs(source.getX() - dest.getY()), Math.abs(source.getY() - dest.getY()));
@@ -88,7 +118,9 @@ public class GraphPanel<V, W extends Number> extends Component {
             edgeComponent.setBounds(edgeRender.getBox(edgeComponent, center));
             edges.add(edgeComponent);
             graph.addEdge(edgeComponent.edge);
-        } catch (Exception ignore) {}
+        } catch (Exception ignore) {
+        	ignore.printStackTrace();
+        }
     }
 
     public void removeEdge(VertexComponent<V> source, VertexComponent<V> dest) {
@@ -128,6 +160,26 @@ public class GraphPanel<V, W extends Number> extends Component {
         observers.remove(observer);
     }
 
+    public void save(String fileName) throws IOException {
+    	GraphGraphicalSave save = new GraphGraphicalSave(vertices);
+    	Graph.save(graph, Graph.GSON.toJson(save), fileName);
+    }
+    
+    public void load(String fileName) throws IOException {
+    	String saveContent = Graph.load(graph, fileName);
+    	GraphGraphicalSave save = Graph.GSON.fromJson(saveContent, GraphGraphicalSave.class);
+    	vertices.removeAll();
+    	edges.removeAll();
+    	
+    	for(int i = 0; i<save.vertices.size(); i++) {
+    		V v = save.vertices.get(i);
+    		Point p = save.points.get(i);
+    		addVertex(p, v);
+    	}
+    	save.vertices.forEach(v -> graph.getEdgesOut(v).forEach(e -> addEdge(e)));
+    	
+    	repaint();
+    }
 
     @Override
     public void setBounds(int x, int y, int width, int height) {
@@ -170,5 +222,20 @@ public class GraphPanel<V, W extends Number> extends Component {
     private void updateObservers() {
         observers.forEach(observer -> observer.update(null, this.graph));
     }
-
+    
+    class GraphGraphicalSave {
+    	public GraphGraphicalSave() {}
+    	protected GraphGraphicalSave(Container vertices) {
+    		this.vertices = new LinkedList<>();
+    		this.points = new LinkedList<>();
+    		
+        	for(Component vertex : vertices.getComponents()) {
+    			this.points.add(new Point(vertex.getX(), vertex.getY()));
+    			this.vertices.add(((VertexComponent<V>) vertex).vertex.getValue());
+        	}
+    	}
+    	
+    	public List<V> vertices;
+    	public List<Point> points;
+    }
 }
diff --git a/src/berack96/sim/util/graph/view/vertex/VertexComponent.java b/src/berack96/sim/util/graph/view/vertex/VertexComponent.java
index 8cd00c0..3502cf8 100644
--- a/src/berack96/sim/util/graph/view/vertex/VertexComponent.java
+++ b/src/berack96/sim/util/graph/view/vertex/VertexComponent.java
@@ -12,4 +12,19 @@ public class VertexComponent<V> extends Component {
     public VertexComponent(Vertex<V> vertex) {
         this.vertex = vertex;
     }
+    
+    
+    @Override
+    public String toString() {
+    	return "[" + vertex + " {" + getX() + "," + getY() + "}]";
+    }
+    
+    @Override
+    public boolean equals(Object obj) {
+    	try {
+    		return obj.getClass().equals(getClass()) && obj.toString().equals(toString());	
+    	} catch (Exception e) {
+    		return false;
+    	}
+    }
 }
diff --git a/test/berack96/test/sim/TestGraph.java b/test/berack96/test/sim/TestGraph.java
index 48e31d6..03313ee 100644
--- a/test/berack96/test/sim/TestGraph.java
+++ b/test/berack96/test/sim/TestGraph.java
@@ -64,6 +64,7 @@ public class TestGraph {
     public void after() {
     	try {
 			String printed = bytes.toString(encoding);
+			bytes.reset();
 			if (!printed.isEmpty())
 				fail("Remove the printed string in the methods: " + printed);
 		} catch (UnsupportedEncodingException e) {
@@ -1186,6 +1187,10 @@ public class TestGraph {
                 new Edge<>("5", "4", 5),
                 new Edge<>("6", "2", 2));
         
+        sub = graph.subGraph();
+        shouldContain(sub.vertices(), "7", "8");
+        shouldContain(sub.edges(), new Edge<>("8", "7", 9));
+        
         sub = graph.subGraph(null);
         shouldContain(sub.vertices(), "7", "8");
         shouldContain(sub.edges(), new Edge<>("8", "7", 9));
@@ -1325,37 +1330,54 @@ public class TestGraph {
          */
 
     	String fileName = "test/resources/test.json";
+    	Set<String> vertices = new HashSet<>();
+    	Set<Edge<String, Integer>> edges = new HashSet<>();
     	
-        graph.addVertexIfAbsent("1");
-        graph.addVertexIfAbsent("2");
-        graph.addVertexIfAbsent("3");
-        graph.addVertexIfAbsent("4");
-        graph.addVertexIfAbsent("5");
-        graph.addVertexIfAbsent("6");
-        graph.addVertexIfAbsent("7");
-        graph.addVertexIfAbsent("8");
+    	vertices.add("1");
+    	vertices.add("2");
+    	vertices.add("3");
+    	vertices.add("4");
+    	vertices.add("5");
+    	vertices.add("6");
+    	vertices.add("7");
+    	vertices.add("8");
 
-        graph.addEdge("1", "2", 1);
-        graph.addEdge("1", "3", 1);
-        graph.addEdge("2", "5", 4);
-        graph.addEdge("4", "6", 6);
-        graph.addEdge("5", "3", 2);
-        graph.addEdge("5", "4", 5);
-        graph.addEdge("6", "2", 2);
-        graph.addEdge("8", "7", 9);
+    	edges.add(new Edge<>("1", "2", 1));
+    	edges.add(new Edge<>("1", "3", 1));
+    	edges.add(new Edge<>("2", "5", 4));
+    	edges.add(new Edge<>("4", "6", 6));
+    	edges.add(new Edge<>("5", "3", 2));
+    	edges.add(new Edge<>("5", "4", 5));
+    	edges.add(new Edge<>("6", "2", 2));
+    	edges.add(new Edge<>("8", "7", 9));
+    	
+        graph.addAllVertices(vertices);
+        graph.addAllEdges(edges);
+        
+        /* because GSON convert to double */
+        /*
+        Set<Edge<String, Double>> edgesD = new HashSet<>();
+        edges.forEach((e) -> edgesD.add(new Edge<String, Double>(e.getSource(), e.getDestination(), e.getWeight().doubleValue())));
+        */
+        Set<Edge<String, Integer>> edgesD = edges;
         
         try {
 			Graph.save(graph, fileName);
-			Graph.load(graph, fileName);
+			Graph.load(graph, fileName, String.class, Integer.class);
+			shouldContain(graph.vertices(), vertices.toArray());
+			shouldContain(graph.edges(), edgesD.toArray());
+			
 			graph.removeAllVertex();
-			Graph.load(graph, fileName);
+			Graph.load(graph, fileName, String.class, Integer.class);
+			shouldContain(graph.vertices(), vertices.toArray());
+			shouldContain(graph.edges(), edgesD.toArray());
 		} catch (Exception e) {
 			fail(e.getMessage());
 		}
         
 		graph = null;
 		shouldThrow(new NullPointerException(), () -> { try {
-			Graph.load(graph, fileName);
+			Graph.load(graph, fileName, String.class, Integer.class);
 		} catch (IOException e) {
 			fail();
 			e.printStackTrace();
diff --git a/test/resources/test.json b/test/resources/test.json
index eb6138f..a35f98b 100644
--- a/test/resources/test.json
+++ b/test/resources/test.json
@@ -1 +1 @@
-{"vertices":["1","2","3","4","5","6","7","8"],"edges":[{"source":"1","destination":"2","weight":1},{"source":"1","destination":"3","weight":1},{"source":"5","destination":"4","weight":5},{"source":"6","destination":"2","weight":2},{"source":"5","destination":"3","weight":2},{"source":"8","destination":"7","weight":9},{"source":"4","destination":"6","weight":6},{"source":"2","destination":"5","weight":4}]}
\ No newline at end of file
+{"vertices":["1","2","3","4","5","6","7","8"],"edges":[{"source":"1","destination":"2","weight":1},{"source":"1","destination":"3","weight":1},{"source":"5","destination":"4","weight":5},{"source":"6","destination":"2","weight":2},{"source":"5","destination":"3","weight":2},{"source":"8","destination":"7","weight":9},{"source":"4","destination":"6","weight":6},{"source":"2","destination":"5","weight":4}],"other":""}
\ No newline at end of file