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  1. import java.util.List;
  2. import java.util.Map;
  3. import java.util.stream.Collectors;
  4. import static java.util.Map.entry;
  5.  
  6. public final class Main {
  7.  
  8.     private static final Map<String, Runnable> COMMAND_MAP = Map.ofEntries(
  9.             entry("help", () -> printHelp()),
  10.             entry("quit", () -> exitProgram()),
  11.             entry("shutdown", () -> shutdownSystem()));
  12.  
  13.     private static void printHelp() {
  14.         System.out.println("printHelp");
  15.     }
  16.  
  17.     private static void exitProgram() {
  18.         System.out.println("exitProgram");
  19.     }
  20.  
  21.     private static void shutdownSystem() {
  22.         System.out.println("shutdownSystem");
  23.     }
  24.  
  25.     private static List<String> getCommandList() {
  26.         return List.of("help", "reboot", "shutdown");
  27.     }
  28.  
  29.     private static void fixMe() {
  30.         var list = getCommandList().stream()
  31.             // Defers disposition of 'null' when 'Map#get(Object)' returns
  32.             // 'null'
  33.             .map(COMMAND_MAP::get)
  34.             // The next statement is equivalent to '.filter(Objects::nonNull)'
  35.             .filter(r -> r != null)
  36.             .collect(Collectors.toList());
  37.         list.forEach(r -> r.run());
  38.     }
  39.  
  40.     public static void main(String[] args) {
  41.         fixMe();
  42.     }
  43. }
  44.  
Success #stdin #stdout 0.08s 34180KB
comments (?)
stdin
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Standard input is empty
stdout
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printHelp
shutdownSystem
https://ideone.com/ZWEj6t
The Insanity Beyond Null: Exercise 2 (Java)
language:
Java (HotSpot 12)
created:
3 years ago
visibility:
public

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