java-Graphstream查看器不出现

Question

我正在使用graphstream库，以便使用Java构建可视化图形应用程序。我想在从jframe扩展的类中加载图形。问题是我发现的documentation很旧，没有找到其他文档。 这是我代码的一部分，我要从现有文件中加载图形：

package tutographstream;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.Toolkit;
import java.io.FileReader;
import java.util.Scanner;
import javax.swing.JFrame;
import javax.swing.JPanel;
import org.graphstream.graph.Graph;
import org.graphstream.graph.Node;
import org.graphstream.graph.implementations.SingleGraph;
import org.graphstream.ui.swingViewer.ViewPanel;
import org.graphstream.ui.view.Viewer;

public class MainViewer extends JFrame{

    Graph graph = null;
    Viewer viewer = null;

    public MainViewer(){
        initComponents();
    }

    void initComponents(){   
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        Dimension DimMax = Toolkit.getDefaultToolkit().getScreenSize();
        setMaximumSize(DimMax);
        setExtendedState(JFrame.MAXIMIZED_BOTH);  

        graphViewerJPanel = new JPanel(new GridLayout()){
            @Override
            public Dimension getPreferredSize() {
                return new Dimension(700, 700);
            }
        };

        graphViewerJPanel.setBackground(Color.cyan);
        add(graphViewerJPanel);

    }

    public Graph buildGraph(String filepath, int N){

        double[][] mat = null;
        try {
            mat = new double[N][N];
            Scanner sc = new Scanner(new FileReader(filepath));
            int counter = 0;
            while(sc.hasNext()){
                mat[counter / N][counter % N] = Double.valueOf(sc.next());
                counter++;
            }

            graph = new SingleGraph("Tutorial 1", false, true);

            for(int i=0; i<N; i++) {                       
                graph.addNode("A"+i);                                    
            }

            for(int i=0; i<N; i++)
                for(int j=i; j<N; j++)
                    if(mat[i][j] != 0)
                        graph.addEdge(""+(i*N+j), "A"+i, "A"+j);                        

            int index=0;
            for(Node node:graph.getNodeSet()){
                node.addAttribute("ui.label", ""+index);
                node.addAttribute("ui.style", "shape:circle; size:30px; text-alignment: center;");
                index++;
            }

        } catch (Exception e) {
            System.out.println("Error: "+e.getMessage());
        }

        return graph;
    }

    public Viewer loadGraph(String filepath, int N){
        buildGraph(filepath, N);
        if(graph != null){
            viewer = new Viewer(graph, Viewer.ThreadingModel.GRAPH_IN_GUI_THREAD);
            ViewPanel view_panel = viewer.addDefaultView(false);
            viewer.enableAutoLayout();
            graphViewerJPanel.add(view_panel);    
            repaint();
        }
        else 
            System.out.println(" Error");

        return viewer;
    }

    //main function
    public static void main(String[] args) {        
       int N = 20;        
       String filepath = "files/ErdosReney"+N+".txt";

       MainViewer main_viewer = new MainViewer();
       main_viewer.setVisible(true);

       Viewer viewer = main_viewer.loadGraph(filepath, N);
    }

    //components    
    JPanel graphViewerJPanel;


}

问题在于该图形未显示在jpanel中。