问未排序的primefaces selectOneMenu

EN

    <p:selectOneMenu id="Department" value="#{search.selectedDepartment}">  
            <f:selectItem itemLabel="Select Department" itemValue="" />  
            <f:selectItems value="#{search.departments}" />  

        </p:selectOneMenu> 

public class SearchBean implements Serializable {

private Map<String, Map<String, String>> courseData = new HashMap<String, Map<String, String>>();

private Map<String, String> departments = new HashMap<String, String>();
private String selectedDepartment;


    departments.put("department1",
            "department1");
    departments.put("department2",
            "department2");
    departments.put("department3", "department3");
departments.put("department4", "department4");
departments.put("department5", "department5");





//getters setters...


}