package org.apidesign.singletons.api;

 import java.util.Iterator;

 import java.util.ServiceLoader;

 import org.openide.util.Lookup;

 // BEGIN: singletons.injectable.api

 public abstract class DialogDisplayer {

     protected DialogDisplayer() {

     }

     /** Ask user a question.

      *

      * @param query the text of the question

      * @return true if user confirmed or false if declined

      */

     public abstract boolean yesOrNo(String query);

     public static DialogDisplayer getDefault() {

         return Impl.DEFAULT;

     }

     // FINISH: singletons.injectable.api

     // BEGIN: singletons.injectable.dummyimpl

     private static final class Impl extends DialogDisplayer {

         private static final DialogDisplayer DEFAULT = initialize();

         @Override

         public boolean yesOrNo(String query) {

             System.err.printf("Saying no to '%s'\n", query);

             return false;

         }

         // FINISH: singletons.injectable.dummyimpl

         private static DialogDisplayer initialize() {

             if (Boolean.getBoolean("singleton.jdk6")) {

                 return initializeServiceLoader();

             } else {

                 return initializeLookup();

             }

         }

         // BEGIN: singletons.injectable.serviceloader

         private static DialogDisplayer initializeServiceLoader() {

             // see http://singletons.apidesign.org

             Iterator<DialogDisplayer> it = null;

             it = ServiceLoader.load(DialogDisplayer.class).iterator();

             return it != null && it.hasNext() ? it.next() : new Impl();

         }

         // END: singletons.injectable.serviceloader

         // BEGIN: singletons.injectable.lookup

         private static DialogDisplayer initializeLookup() {

             DialogDisplayer def = Lookup.getDefault().lookup(DialogDisplayer.class);

             return def != null ? def : new Impl();

         }

         // END: singletons.injectable.lookup

     }

 }