Ehm... Credo di aver fatto un po' di casino. Ho modificato la tua classe facendo in modo che ci sia una stringa visualizzata e un intero come valore che serve a me... E' sbagliato, eh?

Qui sotto il codice... Qualche idea?

Grazie!

codice:
// Grazie a simo7784
public class ComboItem{
   private String name;
   private int value;

   /** Permette di associare una stringa (che sarà visualizzata nella comboBox) a un valore**/
   public ComboItem(String name, int value) {
      this.name = name;
      this.value = value;
   }

   public String getName() {
      return name;
   }

   public int getValue() {
      return value;
   }

   public String toString() {
       //la combobox stampa il toString degli oggetti
      return name;
   }
}
codice:
L'eccezione:

Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: java.lang.Integer
        at GUI.NewJFrame.jComboBox1ActionPerformed(NewJFrame.java:371)
        at GUI.NewJFrame.access$000(NewJFrame.java:16)
        at GUI.NewJFrame$1.actionPerformed(NewJFrame.java:101)
        at javax.swing.JComboBox.fireActionEvent(JComboBox.java:1197)
        at javax.swing.JComboBox.contentsChanged(JComboBox.java:1268)
        at javax.swing.AbstractListModel.fireContentsChanged(AbstractListModel.java:100)
        at javax.swing.DefaultComboBoxModel.setSelectedItem(DefaultComboBoxModel.java:88)
        at javax.swing.DefaultComboBoxModel.addElement(DefaultComboBoxModel.java:126)
        at javax.swing.JComboBox.addItem(JComboBox.java:690)
        at GUI.NewJFrame.propOf(NewJFrame.java:627)
        at GUI.NewJFrame.setUp(NewJFrame.java:434)
        at GUI.NewJFrame.jButton2ActionPerformed(NewJFrame.java:401)
        at GUI.NewJFrame.access$200(NewJFrame.java:16)
        at GUI.NewJFrame$3.actionPerformed(NewJFrame.java:136)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1849)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2169)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:420)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:258)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
        at java.awt.Component.processMouseEvent(Component.java:5501)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3135)
        at java.awt.Component.processEvent(Component.java:5266)
        at java.awt.Container.processEvent(Container.java:1966)
        at java.awt.Component.dispatchEventImpl(Component.java:3968)
        at java.awt.Container.dispatchEventImpl(Container.java:2024)
        at java.awt.Component.dispatchEvent(Component.java:3803)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4212)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3892)
        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3822)
        at java.awt.Container.dispatchEventImpl(Container.java:2010)
        at java.awt.Window.dispatchEventImpl(Window.java:1778)
        at java.awt.Component.dispatchEvent(Component.java:3803)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:463)
        at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:242)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)

---------------------------

Questo per riempire la combo:

	caricaCombo(jComboBox1,arrString,arrInt, nEd);


    public void caricaCombo(javax.swing.JComboBox combo, String arrS[], int arrI[], int nEd){
        ComboItem ci[] = new ComboItem[nEd];
        
        if(nEd != 0){
            combo.setEnabled(true);
            combo.removeAllItems();
            //Riempio la comboBox
            for(int i = 0; i< nEd; i++){
                ci[i] = new ComboItem(arrS[i],arrI[i]);
                
                combo.addItem(ci[i]);
            }
        }
    }

---------------------------
Action

    private void jComboBox1ActionPerformed(java.awt.event.ActionEvent evt) {                                           
        int num = 0;
        if((ComboItem)jComboBox1.getSelectedItem()!=null){
            jComboBox2.setEnabled(true);
            ComboItem item = (ComboItem)jComboBox1.getSelectedItem();
            num = item.getValue();
	    ... Lavoro con num...
        }
    }