Di seguito la classe "java"

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/*
* JApplet.java
*
* Created on 22 ottobre 2002, 19.26
*/

/**
*
* @author denis76
*/
public class JApplet extends javax.swing.JApplet {

/** Creates new form JApplet */
public JApplet() {
initComponents();
}

/** This method is called from within the constructor to
* initialize the form.
* WARNING: Do NOT modify this code. The content of this method is
* always regenerated by the Form Editor.
*/
private void initComponents() {
jLabel1 = new javax.swing.JLabel();
jButton1 = new javax.swing.JButton();

jLabel1.setText("jLabel1");
getContentPane().add(jLabel1, java.awt.BorderLayout.CENTER);

jButton1.setText("Clicca qua");
jButton1.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
jButton1ActionPerformed(evt);
}
});

getContentPane().add(jButton1, java.awt.BorderLayout.NORTH);

}

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
jOPInformazioni= new javax.swing.JOptionPane();
jOPInformazioni.showMessageDialog(null, "Eccomi qua!");
jLabel1.setText("Sono una javax.swing.JLabel!!!!!!!!");
}

private javax.swing.JOptionPane jOPInformazioni;
// Variables declaration - do not modify
private javax.swing.JLabel jLabel1;
private javax.swing.JButton jButton1;
// End of variables declaration

}
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//
//
//
//
// Ora la pagina "html"
_________________<html>
<head>
<title>Applet HTML Page</title>
</head>
<body>

<h3><hr WIDTH="100%">Applet HTML Page<hr WIDTH="100%"></h3>




<applet code="JApplet.class" width=350 height=200></applet>
</p>

<hr WIDTH="100%"><font SIZE=-1>Generated by NetBeans IDE</font>

</body>
</html>
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Se la classe, dopo compilazione, nn ti funziona nel tuo Browser, nel mio sito trovi la spiegazione.
Ciao ciao.