String gdate=new String();
//注明,addItem()中用的是字符串
public void itemStateChanged(ItemEvent e){
        if(e.getSource()==f1){   //注明,f1.addItem()中用的是字符串

            gdate=e.getItem();
            b1=Integer.parseInt(gdate);//把字符串gdate转换为int型的
            }
            if(e.getSource()==f2){    //注明,f2.addItem()中添加的选项是字符串               
                gdate=e.getItem();
                b2=Integer.parseInt(gdate);
                }
                if(e.getSource()==f3){   //注明,f3.addItem()中添加的选项是字符串    
                gdate=e.getItem();
                b3=Integer.parseInt(gdate);
                }

程序能编译但,出现这结果:
Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException:javax.swing
at lixi.itemStateChanged(lixi.java:203)// gdate=(String)e.getSource();
at javax.swing.JComboBox.fireItemstateChanged(Unknown Source)
at javax.swing.JComboBox.selectedItemChanged(Unknown Source)
at javax.swing.JComboBox.contentsChanged(Unknown Source)
at javax.swing.AbstravtListModel.fireContenteChanged(Unknown Source)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
请帮忙弄下,是什么原因??其中lixi]为class类,也是文件名