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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.  
  7. import java.util.HashMap;
  8. import java.util.Map;
  9. import java.util.stream.Stream;
  10.  
  11. /* Name of the class has to be "Main" only if the class is public. */
  12. class Ideone
  13. {
  14. 	public static void main (String[] args) throws java.lang.Exception
  15. 	{
  16.         Map < String, Double > map1 =
  17.                 Map.of(
  18.                         "X1" , 1d ,
  19.                         "X2" , 1d
  20.                 );
  21.  
  22.         Map < String, Double > map2 =
  23.                 Map.of(
  24.                         "X1" , 2d ,
  25.                         "X2" , 2d ,
  26.                         "X3" , 7d
  27.                 );
  28.  
  29.         Map < String, Double > map = new HashMap <>();
  30.         Stream
  31.                 .concat( map1.entrySet().stream() , map2.entrySet().stream() )
  32.                 .forEach(
  33.                         stringDoubleEntry ->
  34.                                 map.put(
  35.                                         stringDoubleEntry.getKey() ,                                                                        // key
  36.                                         map.getOrDefault( stringDoubleEntry.getKey() , 0d ) + stringDoubleEntry.getValue() )  // value
  37.                 );
  38.  
  39.         System.out.println( "map = " + map );
  40. 	}
  41. }
Success #stdin #stdout 0.13s 50720KB
comments ()
stdin 
Standard input is empty
stdout 
map = {X1=3.0, X2=3.0, X3=7.0}
https://ideone.com/qqBRde
language:
Java (HotSpot 12)
created:
2 years ago
visibility:
public

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