JButton não aparece

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;
import javax.swing.JEditorPane;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JScrollPane;
import javax.swing.JTextField;
import javax.swing.event.HyperlinkEvent;
import javax.swing.event.HyperlinkListener;
import javax.swing.*;

public class ReadServerFile extends JFrame
{
	private JEditorPane contentsArea;
	private JButton btn;
	
	
	public ReadServerFile()
	{
		super( "Web Browser" );
		
			btn = new JButton("Abrir Arquivo");
			setVisible( true );
			btn.addActionListener(
			new ActionListener()
				{
					public void actionPerformed( ActionEvent event )
					{
						getThePage( event.getActionCommand() );
					}
				}
);								
									contentsArea = new JEditorPane();
									contentsArea.setEditable( false );
									contentsArea.addHyperlinkListener(
										new HyperlinkListener()
										{
											public void hyperlinkUpdate( HyperlinkEvent event )
											{
												if ( event.getEventType() ==
														HyperlinkEvent.EventType.ACTIVATED )
														getThePage( event.getURL().toString() );
											}			
										}
										);
											add( new JScrollPane( contentsArea ), BorderLayout.CENTER );
											setSize( 300, 400 );
											setVisible( true );
}	

	private void getThePage( String location )
	{
		try
			{
				contentsArea.setPage( location );
			}
				catch ( IOException ioException )
				{
					JOptionPane.showMessageDialog( this, 
					"Caminho/URL não encontrado", "Caminho/URL nulo", JOptionPane.ERROR_MESSAGE );
				}
	}
}