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I've written a program which will generate a split window: 
 
public class AVIS extends JSplitPane 
{ 
&nbsp; static &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;JFrame frame; 
&nbsp; private &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;JTextField &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;tf=new JTextField(19); 
 
&nbsp; public AVIS() 
&nbsp; { 
&nbsp; &nbsp; super(HORIZONTAL_SPLIT); 
&nbsp; &nbsp; 
&nbsp; &nbsp; JScrollPane listScrollPane = new JScrollPane(); 
 
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;JTabbedPane &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;tabbedPane=new JTabbedPane(); 
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;tabbedPane.addTab(&quot;Nr.1&quot;, tf); 
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;tabbedPane.addTab(&quot;Nr.2&quot;, tf); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;setLeftComponent(listScrollPane); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp;setRightComponent(tabbedPane); 
&nbsp; &nbsp;setDividerLocation(150); 
&nbsp; &nbsp;setDividerSize(10); 
&nbsp; &nbsp;setPreferredSize(new Dimension(400, 200)); 
&nbsp; } 
 
&nbsp; public static void main(String s[]) 
&nbsp; { 
&nbsp; &nbsp; WindowListener l = new WindowAdapter() 
&nbsp; &nbsp; { 
&nbsp; &nbsp; &nbsp; public void windowClosing(WindowEvent e) &nbsp; &nbsp; &nbsp; {System.exit(0); 
&nbsp; &nbsp; } 
&nbsp; }; 
&nbsp; frame = new JFrame(&quot;AVIS&quot;); 
&nbsp; frame.addWindowListener(l); &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;frame.getContentPane().add(&quot;Center&quot;, new AVIS()); &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;frame.pack(); 
&nbsp; frame.setVisible(true); 
&nbsp; } 
}; 
 
But as I start the program, one can just see a tab &quot;Nr.1&quot;, not two tabs &quot;Nr.1&quot; and &quot;Nr.2&quot;. 
&nbsp;Why?
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I've written a program which will generate a split window:

public class AVIS extends JSplitPane
{
  static	JFrame frame;
  private	JTextField	tf=new JTextField(19);

  public AVIS() 
  {
    super(HORIZONTAL_SPLIT);
    
    JScrollPane listScrollPane = new JScrollPane();

           JTabbedPane	tabbedPane=new JTabbedPane();
		tabbedPane.addTab("Nr.1", tf);
		tabbedPane.addTab("Nr.2", tf);	   setLeftComponent(listScrollPane);		      setRightComponent(tabbedPane);
   setDividerLocation(150);
   setDividerSize(10);
   setPreferredSize(new Dimension(400, 200));
  }

  public static void main(String s[]) 
  {
    WindowListener l = new WindowAdapter() 
    {
      public void windowClosing(WindowEvent e)       {System.exit(0);
    }
  };
  frame = new JFrame("AVIS");
  frame.addWindowListener(l);          frame.getContentPane().add("Center", new AVIS());          frame.pack();
  frame.setVisible(true);
  }
};

But as I start the program, one can just see a tab "Nr.1", not two tabs "Nr.1" and "Nr.2".
 Why?

JSplitPane

Java is a platform-independent, object-oriented programming language and run-time environment, designed to have as few implementation dependencies as possible such that developers can write one set of code across all platforms using libraries. Most devices will not run Java natively, and require a run-time component to be installed in order to execute a Java program.