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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.lang.*;
  5. import java.io.*;
  6. import java.util.stream.*;
  7. import java.util.function.*;
  8.  
  9. /* Name of the class has to be "Main" only if the class is public. */
  10. class Ideone
  11. {
  12. 	public static void main (String[] args) throws java.lang.Exception
  13. 	{
  14. 		List<Function<? super Data, ? extends Comparable>> extractors = new ArrayList<>();
  15.         extractors.add(Data::getA);
  16.         extractors.add(Data::getB);
  17.  
  18.         Comparator<Data> test = parseKeysAscending(extractors);
  19.  
  20.         List<Data> data = new ArrayList<>(Arrays.asList(
  21.         	new Data(1, "z"),
  22.         	new Data(2, "b"),
  23.         	new Data(1, "a")));
  24.  
  25. 		System.out.println(data); // [[1, 'z'], [2, 'b'], [1, 'a']]
  26.  
  27.         data.sort(test);
  28.  
  29. 		System.out.println(data); // [[1, 'a'], [1, 'z'], [2, 'b']]
  30. 	}
  31.  
  32. 	public static <T, S extends Comparable<? super S>> Comparator<T> parseKeysAscending(List<Function<? super T, ? extends S>> keyExtractors) {
  33.         if (keyExtractors.isEmpty()) {
  34.             return (a, b) -> 0;
  35.         } else {
  36.             Function<? super T, ? extends S> firstSortKey = keyExtractors.get(0);
  37.             List<Function<? super T, ? extends S>> restOfSortKeys = keyExtractors.subList(1, keyExtractors.size());
  38.             return Comparator.comparing(firstSortKey).thenComparing(parseKeysAscending(restOfSortKeys));
  39.         }
  40.     }
  41.  
  42.     public static class Data {
  43. 	    private final Integer a;
  44. 	    private final String b;
  45.  
  46. 	    private Data(int a, String b) {
  47. 	        this.a = a;
  48. 	        this.b = b;
  49. 	    }
  50.  
  51. 	    public Integer getA() {
  52. 	        return a;
  53. 	    }
  54.  
  55. 	    public String getB() {
  56. 	        return b;
  57. 	    }
  58.  
  59. 	    @Override
  60. 	    public String toString() {
  61. 	    	return "[" + a + ", '" + b + "']";
  62. 	    }
  63. 	}
  64. }
  65.  
Success #stdin #stdout 0.14s 2184192KB
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stdin
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Standard input is empty
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[[1, 'z'], [2, 'b'], [1, 'a']]
[[1, 'a'], [1, 'z'], [2, 'b']]
https://ideone.com/de7EP5
language:
Java (HotSpot 12)
created:
6 years ago
visibility:
public

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