Java Swing - 如何调整JScrollPane中的GridBagLayout...

import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.JFrame;
import javax.swing.JMenuItem;
import javax.swing.JPopupMenu;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.TreePath;
import javax.swing.tree.TreeSelectionModel;

public class Main extends JFrame {
  public Main() {
    JTree myTree = new JTree();
    myTree.getSelectionModel().setSelectionMode(
        TreeSelectionModel.DISCONTIGUOUS_TREE_SELECTION);

    myTree.addMouseListener(new MyMouseAdapter());

    add(new JScrollPane(myTree));
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    pack();
    setVisible(true);
  }
  public static void main(String[] args) {
    new Main();
  }
}

class MyMouseAdapter extends MouseAdapter {
  private void myPopupEvent(MouseEvent e) {
    int x = e.getX();
    int y = e.getY();
    JTree tree = (JTree) e.getSource();
    TreePath path = tree.getPathForLocation(x, y);
    if (path == null)
      return;

    DefaultMutableTreeNode rightClickedNode = (DefaultMutableTreeNode) path
        .getLastPathComponent();

    TreePath[] selectionPaths = tree.getSelectionPaths();

    boolean isSelected = false;
    if (selectionPaths != null) {
      for (TreePath selectionPath : selectionPaths) {
        if (selectionPath.equals(path)) {
          isSelected = true;
        }
      }
    }
    if (!isSelected) {
      tree.setSelectionPath(path);
    }
    if (rightClickedNode.isLeaf()) {
      JPopupMenu popup = new JPopupMenu();
      final JMenuItem refreshMenuItem = new JMenuItem("refresh");
      refreshMenuItem.addActionListener(ev->System.out.println("refresh!"));
      popup.add(refreshMenuItem);
      popup.show(tree, x, y);
    }
  }

  public void mousePressed(MouseEvent e) {
    if (e.isPopupTrigger())
      myPopupEvent(e);
  }

  public void mouseReleased(MouseEvent e) {
    if (e.isPopupTrigger())
      myPopupEvent(e);
  }
}