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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.util.stream.Collectors;
  5.  
  6. /* Name of the class has to be "Main" only if the class is public. */
  7. class Ideone
  8. {
  9.     public static void main ( String[] args ) throws java.lang.Exception
  10.     {
  11.         List < CountryCount > listOfCountryCount = List.of(
  12.                 new CountryCount( "Peru" , 17L ) ,
  13.                 new CountryCount( "Xanadu" , 128L ) ,
  14.                 new CountryCount( null , 42L ) ,
  15.                 new CountryCount( "Andorra" , null )
  16.         );
  17.  
  18. 		NavigableMap < String, Long > map =
  19. 		        listOfCountryCount
  20. 		                .stream()
  21. 		                .collect(
  22. 		                        Collectors.toMap(
  23. 		                                countryCount -> Objects.isNull( countryCount.getCountry() ) ? "unknown" : countryCount.getCountry() ,
  24. 		                                countryCount -> Objects.isNull( countryCount.getCount() ) ? Long.valueOf( 0 ) : countryCount.getCount() , 
  25. 		                                ( existing , replacement ) -> existing ,  // In case of duplicate key conflict, first one wins.
  26. 		                        		TreeMap :: new 
  27. 		                        )
  28. 		                );
  29.  
  30.         System.out.println( "listOfCountryCount = " + listOfCountryCount );
  31.         System.out.println( "map = " + map );
  32.     }
  33. }
  34.  
  35. final class CountryCount
  36. {
  37.     private final String country;
  38.     private final Long count;
  39.  
  40.     CountryCount ( String country , Long count )
  41.     {
  42.         this.country = country;
  43.         this.count = count;
  44.     }
  45.  
  46.     public String getCountry ( ) { return country; }
  47.  
  48.     public Long getCount ( ) { return count; }
  49.  
  50.     @Override
  51.     public boolean equals ( Object obj )
  52.     {
  53.         if ( obj == this ) return true;
  54.         if ( obj == null || obj.getClass() != this.getClass() ) return false;
  55.         var that = ( CountryCount ) obj;
  56.         return Objects.equals( this.country , that.country ) &&
  57.                 Objects.equals( this.count , that.count );
  58.     }
  59.  
  60.     @Override
  61.     public int hashCode ( )
  62.     {
  63.         return Objects.hash( country , count );
  64.     }
  65.  
  66.     @Override
  67.     public String toString ( )
  68.     {
  69.         return "CountryCount[" +
  70.                 "country=" + country + ", " +
  71.                 "count=" + count + ']';
  72.     }
  73. }
Success #stdin #stdout 0.14s 55312KB
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stdout
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listOfCountryCount = [CountryCount[country=Peru, count=17], CountryCount[country=Xanadu, count=128], CountryCount[country=null, count=42], CountryCount[country=Andorra, count=null]]
map = {Andorra=0, Peru=17, Xanadu=128, unknown=42}
https://ideone.com/4ujNNb
language:
Java (HotSpot 12)
created:
2 years ago
visibility:
public

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