How to get itemId of an item of TreeTable in another class?

Hi,

Items are added into a TreeTable like this:

trtbMain.addItem(new Object[] {v1, v2}, someId);

Note: someId is a guid like d5d78d9e-3b66-4f15-81f6-c70d8ec909a7

Added items are displayed correctly. I'm trying to pass the selected item to another class. The target class has getter and setter as below:

public class TargetClass {

    private com.vaadin.data.Item sourceItem;

    public TargetClass() {}

    protected com.vaadin.data.Item getSourceItem() { return sourceItem; }
    protected void setSourceItem(com.vaadin.data.Item value) { sourceItem=value;  }

}

I pass the selected item to the target class like this:

...
targetClass.setSourceItem(trtbMain.getItem(trtbMain.getValue()));
...

The selected item is passed to the target class succesfully but I couldn't find a way to get the item's id which is a guid. I can see the id in Eclipse in debug mode when i move the mouse pointer on sourceItem. How can I access the item's id?

Thank you...