How can i use an inner Jpanel in another JPanel

Question

Hi, i need to put an inner panel in a container panel.I have been trying for hours but I couldn't make it work. Please waiting for help...
public class Gui extends JFrame{
     public Gui() {
          setDefaultCloseOperation(EXIT_ON_CLOSE);
          setEnabled(true);
          setSize(500, 500);
          JPanel mainPanel=new JPanel();
          int v=ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS;
          int h=ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS;
          JScrollPane jsp=new JScrollPane(mainPanel,v,h);
          this.add(mainPanel);
          setContentPane(jsp);
                //this part doesn't works
          JPanel innerPanel=new JPanel();
          innerPanel.setSize(50, 50);
          innerPanel.setLocation(100, 100);
          innerPanel.setBorder(BorderFactory.createLineBorder(Color.black));
          innerPanel.setBackground(Color.red);
               //this part doesn't works
     public static void main(String[] args) {
          Gui gui= new Gui();
          gui.setVisible(true);
}

Answer 1

I'm sorry it's my bad that i have forgotten to add the innerPanel to mainPannel (But of course i tried it in the original code :) ). Now i made the changes you suggested but there are still problems.
I can see the innerPanel now, but the size and the position of the innerPanel doesn't works.
public Gui() {
          setDefaultCloseOperation(EXIT_ON_CLOSE);
          setEnabled(true);
          setSize(500, 500);
          JPanel mainPanel=new JPanel();
          int v=ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS;
          int h=ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS;
          JScrollPane jsp=new JScrollPane(mainPanel,v,h);
          getContentPane().add(jsp);
          JPanel innerPanel=new JPanel();
          innerPanel.setSize(500, 500);
          innerPanel.setLocation(400, 400);
          innerPanel.setBorder(BorderFactory.createLineBorder(Color.black));
          innerPanel.setBackground(Color.red);
                mainPanel.add(innerPanel);
                //also i tried
                //getContentPane().add(innerPanel);
                //or
                //jsp.add(innerPanel);        
...