How do I create a Pager object?

I'm trying to write a unit test using Mockito and Junit and creating mock objects, and the mock GroupManager has to return a list of users. It returns a Pager object, but Pager is an interface! I even tried to look at GroupManager souce code, but that is also an interface! How do I create a Pager object to return?

The JavaDocs doesn't even have the Pager class!

1 answer

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you found the groupmanager interface. why didn't you continue to look for an implementation class? you can find them close to the interface definitions.

in the impl.* subpackage you will find e.g.the HibernateGroupManager which implements the GroupManager interface.

getGroups() is implemented this way:

public Pager<Group> getGroups() throws EntityException {

        List<Group> result;
        try {
            result = getGroupsFromHibernate();
        catch (DataAccessException e)  {
            throw new RepositoryException(e);

        if (result == null) {
            return DefaultPager.emptyPager();

        return new DefaultPager<Group>(result);

DefaultPager is in the sourcetree too:

public class DefaultPager<T> implements Pager<T> {

    private final List<T> page = new ArrayList<T>();
    private Iterator<T> iter;
    private int index; 

    public static <T> DefaultPager<T> emptyPager() {
        return new DefaultPager<T>(Collections.<T>emptyList());

    /** @deprecated since 2.0.3. Use the generic-friendly emptyPager() method */
    public DefaultPager(){

    public DefaultPager(Collection<T> col){
        if (col != null) {
        iter = page.iterator();

    public boolean isEmpty() {
        if (page == null) return true;
        return page.isEmpty();

    public Iterator<T> iterator() {
        return iter;

     * @return a single, preloaded page.
    public List<T> getCurrentPage() {
        return new ArrayList<T>(page);

    public void nextPage() {
        //do nothing, all contents are already within the currentPage

    public boolean onLastPage() {
        return true;

    public void skipTo(int index) throws PagerException  {
        if (index < 0)
            throw new PagerException("Cannot skipTo a negative amount [" + index + "]"); 

        int originalIndex = this.index;
        int distance;

        if (index > page.size()) {
            distance = page.size();
            this.index = page.size();
        else {
            distance = index - this.index;
            this.index = index;

        for (int i = originalIndex; i < distance; i++);


     * @return the current index position of the pager

    public int getIndex()  {
        return index;

     *  This pager always has all its items in a single page
     * @return zero, because this pager has all its items in a single page
    public int getIndexOfFirstItemInCurrentPage()  {
        return 0;

    public void remove()  {
        throw new UnsupportedOperationException("This iterator does not support removal");

    public boolean hasNext()   {
        return iter.hasNext();

    public T next()    {
        T o =;
        return o;

this should help (-:

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