package api;

 import java.util.ArrayList;

 import java.util.Collection;

 import java.util.Collections;

 import java.util.HashSet;

 import java.util.Iterator;

 import java.util.List;

 import java.util.Set;

 /** Simplified version of NetBeans 

  * <a href="http://bits.netbeans.org/6.0/javadoc/org-openide-util/org/openide/util/Lookup.html">Lookup</a>

  * reimplemented to separate the API for clients

  * from the API for implementators while guaranteeing

  * consistency among all there methods.

  *

  * @author Jaroslav Tulach <jtulach@netbeans.org>

  * @version 2.0

  */

 // BEGIN: design.consistency.2.0

 public abstract class Lookup {

     /** only for classes in the same package */

     Lookup() {

     }

     // BEGIN: design.consistency.lookup.2.0

     public <T> T lookup(Class<T> clazz) {

         Iterator<T> it = doLookup(clazz);

         return it.hasNext() ? it.next() : null;

     }

     // END: design.consistency.lookup.2.0

     // BEGIN: design.consistency.lookupAll.2.0

     public <T> Collection<? extends T> lookupAll(Class<T> clazz) {

         Iterator<T> it = doLookup(clazz);

         if (!it.hasNext()) {

             return Collections.emptyList();

         } else {

             List<T> result = new ArrayList<T>();

             while (it.hasNext()) {

                 result.add(it.next());

             }

             return result;

         }

     }

     // END: design.consistency.lookupAll.2.0

     // BEGIN: design.consistency.lookupAllClasses.2.0

     public <T> Set<Class<? extends T>> lookupAllClasses(Class<T> clazz) {

         Iterator<T> it = doLookup(clazz);

         if (!it.hasNext()) {

             return Collections.emptySet();

         } else {

             Set<Class<? extends T>> result = 

                 new HashSet<Class<? extends T>>();

             while (it.hasNext()) {

                 result.add(it.next().getClass().asSubclass(clazz));

             }

             return result;

         }

     }

     // END: design.consistency.lookupAllClasses.2.0

 // FINISH: design.consistency.2.0

     abstract <T> Iterator<T> doLookup(Class<T> clazz);

 }