Scrolling panel

Question

I have a customized panel by overriding the "paintComponent" method in the "MyPanel" class, which can display a heatmap graph when executing the program. I put the panel inside a scrollpane, then displayed in a dialog. The code in my dialog class is like following:
private void createGUI() throws Exception{
    MyPanel mypanel = new MyPanel(node.data);
    JScrollPane scrollPane = new JScrollPane(mypanel);
    scrollPane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
    scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
    this.getContentPane().add(scrollPane);
    setSize(150, 50);
    setLocationRelativeTo(null);
    setVisible(true);
  }The problem is that when the displayed graph is large, I want to scroll the panel, but this does not work.
It seems that the scroll bar is freezen and can't move either horizontally or vertically.
Hope you could give some advice on this problem. Your help is greatly appreciated!

Answer 1

Thank you very much for the answer!
It works after setting the preferred size for the panel as you suggested, however, I'm not sure why I should do that.
The only problem happens when I was diplaying big heatmap graph, (for e.g, like 100,000 rows and 3 columns of float data). Heatmap is a graph that can convert and display data in a color map. When I move the vertical scroll bar, the heatmap graph will change from vertical to horizontal displayed, and when I move to the bottom of the graph, the graph will disappear. In another words, I can't use scroll bar to move smoothly and corretly for the big heatmap graph. Hope I could get some advice on this issue.
Your help is highly appreciated.
Jenny