SimpleComboBox

final SimpleComboBox<String> cascade = new SimpleComboBox<String>();  
    cascade.setTriggerAction(TriggerAction.ALL);  
    cascade.setEditable(false);  
    cascade.add("Parent");  
    cascade.add("Children");  
    cascade.add("None");  
    cascade.setSimpleValue("Parent");  
    cascade.addListener(Events.Change, new Listener<FieldEvent>() {  
      public void handleEvent(FieldEvent be) {  
        String val = cascade.getSimpleValue();  
        if ("Parent".equals(val)) {  
          tree.setCheckStyle(CheckCascade.PARENTS);  
        } else if ("Children".equals(val)) {  
          tree.setCheckStyle(CheckCascade.CHILDREN);  
        } else {  
          tree.setCheckStyle(CheckCascade.NONE);  
        }  
      }  
    });