JTabbedPane

create tabs:

JTabbedPane tp = new JTabbedPane();
tp.addTab("Tab 1", new JPanel());
tp.addTab("Tab 2", new JPanel());

react to the tab-change:

JTabbedPane tp = new JTabbedPane();
//... (add tabs)
tp.addChangeListener(new ChangeListener() {
   stateChanged(ChangeEvent e) { 
   JTabbedPane tp = (JTabbedPane)e.getSource();
   int indx = tp.getSelectedIndex(); 
   // indx identifys the selected tab.
}