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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.time.DayOfWeek;
  4. import java.util.List;
  5. import java.util.Map;
  6. import java.util.concurrent.*;
  7.  
  8. /* Name of the class has to be "Main" only if the class is public. */
  9. class Ideone
  10. {
  11.     public static void main ( String[] args )
  12.     {
  13.         Ideone app = new Ideone();
  14.         app.demo();
  15.     }
  16.  
  17.     private void demo ( )
  18.     {
  19.         ExecutorService executorService = Executors.newCachedThreadPool();
  20.         Map < String, DayOfWeek > inputs =
  21.                 Map.of(
  22.                         "Alice" , DayOfWeek.MONDAY ,
  23.                         "Bob" , DayOfWeek.TUESDAY
  24.                 );
  25.  
  26.         ConcurrentMap < String, DayOfWeek > map = new ConcurrentHashMap <>( inputs );
  27.         System.out.println( "INFO - Before: map = " + map );
  28.  
  29.         Repository repository = new Repository();
  30.  
  31.         Callable < DayOfWeek > task = ( ) -> { return map.computeIfAbsent( "Carol" , ( String personNameKey ) -> {return repository.fetchDayOfWeekForPersonName( personNameKey ); } ); };
  32.         List < Callable < DayOfWeek > > tasks = List.of( task , task , task , task , task );
  33.         List < Future < DayOfWeek > > futures = List.of();
  34.         try
  35.         {
  36.             futures = executorService.invokeAll( tasks );
  37.         }
  38.         catch ( InterruptedException e )
  39.         {
  40.             e.printStackTrace();
  41.         }
  42.  
  43.         executorService.shutdown();
  44.         try { executorService.awaitTermination( 10 , TimeUnit.SECONDS ); } catch ( InterruptedException e ) { e.printStackTrace(); }
  45.  
  46.         System.out.println( "INFO - After: map = " + map );
  47.         futures.stream().forEach( dayOfWeekFuture -> {
  48.             try
  49.             {
  50.                 System.out.println( dayOfWeekFuture.get() );
  51.             }
  52.             catch ( InterruptedException e )
  53.             {
  54.                 e.printStackTrace();
  55.             }
  56.             catch ( ExecutionException e )
  57.             {
  58.                 e.printStackTrace();
  59.             }
  60.         } );
  61.     }
  62.  
  63.     class Repository
  64.     {
  65.         public DayOfWeek fetchDayOfWeekForPersonName ( final String personName )
  66.         {
  67.             return DayOfWeek.THURSDAY;
  68.         }
  69.     }
  70. }
  71.  
Success #stdin #stdout 0.11s 60340KB
comments (?)
stdin 
Standard input is empty
stdout 
INFO - Before: map = {Bob=TUESDAY, Alice=MONDAY}
INFO - After: map = {Bob=TUESDAY, Alice=MONDAY, Carol=THURSDAY}
THURSDAY
THURSDAY
THURSDAY
THURSDAY
THURSDAY
https://ideone.com/dHb26p
language:
Java (HotSpot 12)
created:
3 years ago
visibility:
public

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