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  1. import java.time.format.DateTimeFormatter;
  2. import java.time.YearMonth;
  3. import java.util.HashMap;
  4. import java.util.Map;
  5. import java.util.stream.Collectors;
  6. import java.util.stream.Stream;
  7.  
  8. class Main {
  9. 	public static void main(String[] args) {
  10. 		Map<String, Long> expectedValues = new HashMap<>();
  11. 		expectedValues.put("2021-06-01", 10L);
  12. 		expectedValues.put("2021-07-01", 20L);
  13. 		expectedValues.put("2021-08-01", 30L);
  14.  
  15. 		expectedValues = transform(expectedValues);
  16.  
  17. 		// Show the map, sorted by date
  18. 		expectedValues.entrySet().stream()
  19. 		    .sorted(Map.Entry.comparingByKey())
  20. 		    .forEach(e -> System.out.println(e.getKey() + ": " + e.getValue()));
  21. 	}
  22.  
  23. 	private static Map<String, Long> transform(Map<String, Long> expectedValues) {
  24. 		DateTimeFormatter format = DateTimeFormatter.ISO_LOCAL_DATE;
  25. 		return Stream.iterate(YearMonth.now(), ym -> ym.minusMonths(1))
  26. 		    .limit(12)
  27. 		    .map(ym -> ym.atDay(1).format(format))
  28. 		    .map(str -> Map.entry(str, expectedValues.getOrDefault(str, 0L)))
  29. 		    .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
  30. 	}
  31. }
Success #stdin #stdout 0.17s 55528KB
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stdin
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Standard input is empty
stdout
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2020-10-01: 0
2020-11-01: 0
2020-12-01: 0
2021-01-01: 0
2021-02-01: 0
2021-03-01: 0
2021-04-01: 0
2021-05-01: 0
2021-06-01: 10
2021-07-01: 20
2021-08-01: 30
2021-09-01: 0
https://ideone.com/ulAKh3
language:
Java (HotSpot 12)
created:
4 years ago
visibility:
public

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