<applet code="AppletURL.class" width="150" height="20">
   <param name=etic1 value="Java">
   <param name=link1 value="http://www.valentinocondoluci.it/appunti/java">
   <param name=etic2 value="Html">
   <param name=link2 value="http://www.valcon.it/htmleco">
   <param name=etic3 value="IOI">
   <param name=link3 value="http://www.valcon.it/ioi">
</applet>

<applet code="AppletURL.class" width="250" height="30">
   <param name=etic1 value="Java">
   <param name=link1 value="http://www.valentinocondoluci.it/appunti/java">
   <param name=etic2 value="Html">
   <param name=link2 value="http://www.valcon.it/htmleco">
   <param name=etic3 value="IOI">
   <param name=link3 value="http://www.valcon.it/ioi">
</applet>

<applet code="AppletURL.class" width="400" height="30">
   <param name="etic1" value="la Repubblica">
   <param name="link1" value="http://www.repubblica.it">
   <param name="etic2" value="Corriere della Sera">
   <param name="link2" value="http://www.corriere.it">
   <param name="etic3" value="LA STAMPA">
   <param name="link3" value="http://www.lastampa.it">
</applet>

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import java.net.*;

public class AppletURL extends    Applet
                       implements ActionListener
{ 
   String l1, l2, l3, //link
          e1, e2, e3; //etichette
   URL    u1, u2, u3; //url

   public void init()
   {
      l1=getParameter("link1"); e1=getParameter("etic1");
      l2=getParameter("link2"); e2=getParameter("etic2");
      l3=getParameter("link3"); e3=getParameter("etic3"); 

      try
      {
         u1=new URL(l1);
         u2=new URL(l2);
         u3=new URL(l3);
      }
      catch(MalformedURLException ex)
      {
         System.out.println("Problemi con i parametri?");
      }

      setLayout(new GridLayout(1, 3, 0, 0)); // i pulsanti occupano tutto lo spazio

      Button b1=new Button(e1); b1.addActionListener(this); add(b1);
      Button b2=new Button(e2); b2.addActionListener(this); add(b2);
      Button b3=new Button(e3); b3.addActionListener(this); add(b3);
   }

   public void actionPerformed(ActionEvent ae)
   {
      String nome=ae.getActionCommand(); 

           if(nome.equals(e1)) getAppletContext().showDocument(u1);
      else if(nome.equals(e2)) getAppletContext().showDocument(u2);
      else if(nome.equals(e3)) getAppletContext().showDocument(u3);
      else                     System.out.println("Problemi con i pulsanti?");
   }
}

1. <param name="..." value="...">

2. getParameter()

3. URL, MalformedURLException

4. getAppletContext().showDocument()