Theist what ever you want to get or to add that must be belong to Select item class or that type always return List
See this code here
public void setSelectSection(String selectSection) {
this.selectSection = selectSection;
}
public List<SelectItem> getSelectSelectioncatagorey() {
selectSelectioncatagorey = new ArrayList<SelectItem>();
selectSelectioncatagorey.add(new SelectItem("", "Select Catagorey"));
selectSelectioncatagorey.add(new SelectItem("PIN", "PIN"));
selectSelectioncatagorey.add(new SelectItem("PRN", "PRN"));
return selectSelectioncatagorey;
}