Jung Graph不会显示在Jpanel上

我正在使用NetBeans创建一个应该能够显示图形的SWING应用程序 . 在演示应用程序中，我能够使用以下代码在JFrame上显示生成的JUNG图：

UndirectedGraph t = GraphML.CreateGraph("treeAttribute.graphml");
VisualizationViewer<Node, Edge> vv = new VisualizationViewer<Node, Edge>((new FRLayout<Node, Edge>(t)));
vv.getRenderContext().setVertexFillPaintTransformer(new VertexPainter());
vv.getRenderContext().setVertexLabelTransformer(new ToStringLabeller<Node>());
vv.getRenderContext().setEdgeLabelTransformer(new ToStringLabeller<Edge>());

final JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
frame.getContentPane().add(vv);
frame.pack();
frame.setVisible(true);

现在我想使用Palette和设计模式，所以我创建了一个JFrame，并在其中插入了一个JPanel . 我希望我的图形显示在JPanel中，所以我已经将图形的代码插入到initComponents（）方法中 . 代码如下所示：

public class Main extends javax.swing.JFrame {


public Main() throws ParserConfigurationException, SAXException, IOException {
    initComponents();

}

@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">                          
private void initComponents() {

    jPanel1 = new javax.swing.JPanel();
    jLabel1 = new javax.swing.JLabel();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

    javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
    jPanel1.setLayout(jPanel1Layout);
    jPanel1Layout.setHorizontalGroup(
        jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGap(0, 634, Short.MAX_VALUE)
    );
    jPanel1Layout.setVerticalGroup(
        jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGap(0, 298, Short.MAX_VALUE)
    );

    jLabel1.setText("Graph A");

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addContainerGap()
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addComponent(jLabel1)
                .addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
            .addContainerGap(45, Short.MAX_VALUE))
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addGap(39, 39, 39)
            .addComponent(jLabel1)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addContainerGap(42, Short.MAX_VALUE))
    );

    try {

        UndirectedGraph t = GraphML.CreateGraph("treeAttribute.graphml");
        VisualizationViewer<Node, Edge> vv = new VisualizationViewer<Node, Edge>((new FRLayout<Node, Edge>(t)));
        vv.getRenderContext().setVertexFillPaintTransformer(new VertexPainter());
        vv.getRenderContext().setVertexLabelTransformer(new ToStringLabeller<Node>());
        vv.getRenderContext().setEdgeLabelTransformer(new ToStringLabeller<Edge>());
        jPanel1.add(vv);

    } catch (ParserConfigurationException ex) {
        Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
    } catch (SAXException ex) {
        Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
    } catch (IOException ex) {
        Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
    }

    pack();
}// </editor-fold>                        

/**
 * @param args the command line arguments
 */
public static void main(String args[]) {

    try {
        for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
            if ("Nimbus".equals(info.getName())) {
                javax.swing.UIManager.setLookAndFeel(info.getClassName());
                break;
            }
        }
    } catch (ClassNotFoundException ex) {
        java.util.logging.Logger.getLogger(Main.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
        java.util.logging.Logger.getLogger(Main.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(Main.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(Main.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }
    //</editor-fold>

    /* Create and display the form */
    java.awt.EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                new Main().setVisible(true);


            } catch (ParserConfigurationException ex) {
                Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
            } catch (SAXException ex) {
                Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
            } catch (IOException ex) {
                Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
            }

        }
    });

}

// Variables declaration - do not modify                     
private javax.swing.JLabel jLabel1;
private javax.swing.JPanel jPanel1;
// End of variables declaration                   
}

该程序正常运行，但没有任何内容显示在JPanel中 . 我没有收到任何错误或警告，图表就在那里，因为它打印了一些顶点和边缘的信息 . 有什么想法吗？