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  1. import java.util.*;
  2. import java.util.stream.*;
  3.  
  4.  
  5. class O {
  6. 	private final int id;
  7. 	public O(final int id) { this.id = id; }
  8. 	@Override public String toString() { return "" + id; }
  9. }
  10.  
  11. class Ideone {
  12. 	private static final O[] array = new O[]{
  13. 		new O(1),
  14. 		new O(2),
  15. 		new O(3),
  16. 		new O(4)
  17. 	};
  18.  
  19. 	private static Optional<O> retrieve(final int id) {
  20. 		if(id >= 0 && id < array.length)
  21. 			return Optional.of(array[id]);
  22. 		else
  23. 			return Optional.ofNullable(null);
  24. 	}
  25.  
  26. 	private static List<O> get(final List<Integer> ids) {
  27. 		final List<O> result = new ArrayList<O>();
  28.     	for(final int id : ids) {
  29.     		final Optional<O> o = retrieve(id);
  30.     		if(o.isPresent())
  31.     			result.add(o.get());
  32.     		else
  33.     			System.out.println("[Error] Invalid ID: " + id);
  34.     	}
  35.     	return result;
  36. 	}
  37.  
  38.     public static void main(final String[] arguments) {
  39.     	final List<Integer> ids = Arrays.asList(0, 1, 2, 3, 4, 5, 6, 7, 8);
  40. 		final List<O> objects = get(ids);
  41.         System.out.println("Objects: [" + String.join(", ", objects.stream().map(Object::toString).collect(Collectors.toList())) + "]");
  42.     }
  43. }
  44.  
Success #stdin #stdout 0.13s 36792KB
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Standard input is empty
stdout
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[Error] Invalid ID: 4
[Error] Invalid ID: 5
[Error] Invalid ID: 6
[Error] Invalid ID: 7
[Error] Invalid ID: 8
Objects: [1, 2, 3, 4]
https://ideone.com/6h3wn1
language:
Java (HotSpot 12)
created:
4 years ago
visibility:
public

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