NullPointerException « JTree « Java Swing Q&A

1. validate() tree throws NullPointerException on L&F change?    stackoverflow.com

public class TabbedArea extends JTabbedPane {
  public void addArea(){
    add(component);
    final JPanel panel = new JPanel(new BorderLayout());
    panel.add(new JLabel(title), BorderLayout.LINE_START);
  ...

2. null pointer exception while closing a node of jtree    coderanch.com

Object obj = node.getUserObject(); at the above line my application is throwing an exception , i had make ftp app , so whenever i close any of the tree's node , remember that icon that we use to close the jtree's node the one which has leaf nodes inside it , but i m not getting why is it throwing an ...

3. NullPointerException with JTree.setModel()    forums.oracle.com