I would like to use the example from the primefaces showcase to group selectItems in selectOneMenu:

<h:outputText value="Grouping: " />  
    <p:selectOneMenu value="#{formBean.car}">  
        <f:selectItem itemLabel="Select One" itemValue="" />  
        <f:selectItems value="#{formBean.cars}" />  
    </p:selectOneMenu>

My problem is, that there is no implementation of the bean. Now I don't know, how to implement the grouping of the selectItems inside the method getCars(). And I can't find any other example.

jsf-2 primefaces selectonemenu
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