What's wrong with this code?

<javacode>
package com.wipro.security.ssc.config.applets;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.tree.*;
import java.util.Vector;

public class SampleTree extends JApplet {
//Declarations...
JPanel panel1 = null;
JTree jt = null;
JScrollPane jsp = null;
DefaultMutableTreeNode root = null;
DefaultMutableTreeNode node1 = null;
DefaultMutableTreeNode node2 = null;
DefaultMutableTreeNode node3 = null;

private JPanel get_panel1() {
if (panel1 == null) {
panel1 = new JPanel();
panel1.setName("panel1");
panel1.setLayout(null);
get_panel1().add(getSampleTree());
}
return panel1;
}
private JScrollPane getSampleTree() {
if (root == null){
root = new DefaultMutableTreeNode("AOC");
node1 = new DefaultMutableTreeNode("ServerName");
node2 = new DefaultMutableTreeNode("PolicyDomainID");
node3 = new DefaultMutableTreeNode("LicenseKey");
root.add(node1);
root.add(node2);
root.add(node3);
jt = new JTree(root);
DefaultTreeCellRenderer tcr = (DefaultTreeCellRenderer)jt.getCellRenderer(); tcr.setTextSelectionColor(Color.red);

JScrollPane jsp = new JScrollPane(jt);
jsp.setPreferredSize(new Dimension(200, 300));
}
return jsp;
}
public void init(){
setName("Login");
setSize(426, 240);
setContentPane(get_panel1());
}
public void start() { super.start(); }

public void stop() { super.stop(); }

public void destroy() { super.destroy(); }

}
</javacode>
While i try to run this code in Netscape I get an error: java.lang.NullPointerException : trying to get field at offset 0
at get_pane1() and init() methods.

I am new to Swing, so pls dont get irritated if its a silly mistake!

TIA,

Parag.