this is my controller code

public void returnSelectedFields() {   // show selected fields from availabel list to selected list
        System.debug('selcted size in controller :'+selected.size());
        if(selectedFieldOptions == null){
            selectedFieldOptions = new list<SelectOption>();// selected fields in this list
        } 
        Set<String> selectedFieldSet = new Set<String>(selected);       // getting selected fields into string set to remove 
        for(String str : selectedFieldSet) {
            for(integer j = 0; j<availableFieldOptions.size(); j++) {
                if(str == availableFieldOptions[j].getvalue()) {
                    selectedFieldOptions.add(new selectOption(availableFieldOptions[j].getvalue(), availableFieldOptions[j].getLabel()));
                    availableFieldOptions.remove(j);
                }
            }
        }
        if(availableFieldOptions.size()==0) {
            addHide = true; 
        }
        if(selectedFieldOptions.size() > 0) {
            removeHide = false;
            processHide = false;
        }
        selectedFieldOptions.sort();
        availableFieldOptions.sort();
    }
    public void removeSelectedFields() {   // for remove selected fields from second picklist and add them into to second pikclist
        Set<String> removeFieldSet = new Set<String>(remove);   // getting selected fields into string set to remove 
        for(String str : removeFieldSet) {  // removing fields from selected fields
            for(integer j = 0; j<selectedFieldOptions.size(); j++) {
                if(str == selectedFieldOptions[j].getvalue()){
                    availableFieldOptions.add(new SelectOption(selectedFieldOptions[j].getvalue(), selectedFieldOptions[j].getLabel()));
                    selectedFieldOptions.remove(j);
                }
            }
        }
        if(selectedFieldOptions.size() != 0) {
            removeHide = false;
            processHide = false;
        }
        else {
            removeHide = true;
            processHide = true;
        }
        if(availableFieldOptions.size() > 0) {
            addHide = false;
        }
        availableFieldOptions.sort();
        System.debug('availableFieldOptions size in remove methods : '+availableFieldOptions.size());
        System.debug('selectedFieldOptions size remove methods  : '+selectedFieldOptions.size());
    }


Thank you 
YV