display error message on applet

Trying to display error message on applet if wrong text file name is typed in the myTxtBox

My code so far:-



//<APPLET code=Lou2.class width=400 height=200> </APPLET>


import java.applet.*;
import java.awt.*;
import java.io.*;
import java.net.*;
import java.awt.event.*;
public class Lou2 extends Applet implements ActionListener {
     Label myLabel;
     TextArea myBox;
     TextField myTxtbox; //Added new textbox onto applet into which file name can be typed for 23a.
     Button mybtn;
     public void init() {
          myLabel = new Label(
          "The text area shows the information read from the file on the server");
          myBox = new TextArea("", 4, 20);
          myTxtbox = new TextField(20);
          myTxtbox.setText("readthis.txt");
          mybtn = new Button("Load File into Text Area");
          add(myLabel);
          add(myBox);
          add(myTxtbox);
          add(mybtn);
          mybtn.addActionListener(this);
     } // end of init()
     public void actionPerformed(ActionEvent e) {
          loadFile();
     }//end action performed
     public void loadFile() {
          try {
               URL myURL = new URL(getDocumentBase(), myTxtbox.getText());
               // open file on server
               URLConnection myConn = myURL.openConnection();
               InputStreamReader isr = new InputStreamReader(myConn
                         .getInputStream());
               BufferedReader bufr = new BufferedReader(isr);
               String line;
               line = bufr.readLine(); // read ahead  
               while (line != null) {
                    myBox.append(line + "\n");
                    line = bufr.readLine();
               } // end of while          
          } // end of try
          catch (MalformedURLException me) {
               System.out.println("Bad URL encountered" + me);
          } catch (IOException ioe) {
               System.out.println("IO Exception" + ioe);

          }
     }
} // end of Applet