Question

private void cbdmnstatItemStateChanged(java.awt.event.ItemEvent evt) {
    if(evt.getsource()==getSelectedItem){
        tf1.setFocus(true);
    }        
}

Answer 1

Use this method to set the focus on your textfield.

javax.swing.JComponent#requestFocus()

In your case it would look like:

private void onStateChange(java.awt.event.ItemEvent evt) {
    tf1.requestFocus();
}

UPDATE
This will work for you, if your textfields and combobox-items are static, if they are dynamic it is getting a bit more complicated.

 private void onStateChange(java.awt.event.ItemEvent evt) {
        Object selectedItem = evt.getItem();
        if (selectedItem.equals("X")) {
            jTextField1.requestFocus();
        } else if (selectedItem.equals("Y")) {
            jTextField2.requestFocus();
        } else if (selectedItem.equals("Z")) {
            jTextField3.requestFocus();
        }
    }