Compare two Collections populated with different kinds of objects

user_5696544 0
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I have a performance issue trying to compare two big Collections and I'm looking for some help to find a better way to do that.

The classes:

public class TypeOne {
   private int id;
}

and

public class TypeTwo {
   private int id;
}

The code:

Collection<TypeOne> oneColl = someMethodToPopulateThat();
Collection<TypeTwo> twoColl = anotherMethodToPopulateThat();

// Iterating both collections to match the elements by id
for(TypeOne one : oneColl) {
   for(TypeTwo two : twoColl) {
      if (one.getId().equals(two.getId())) 
         System.out.println(one.getId());
   }
}

I already tried to use some functions of Stream API but I didn't get success. Does anyone have any idea to solve this issue? Please.

Thanks in advance.

collections stream java
1 Answers

tl;dr

ones.stream().forEach(
    one -> System.out.println(
        twos.stream().filter( two -> two.getId() == one.getId() ).findAny().toString()
    )
)

Details

I assume sorting as a NavigableSet will improve performance of our searching, though I’ve not verified this attempt at optimization works.

NavigableSet < TypeOne > ones = new TreeSet <>( Comparator.comparingInt( TypeOne :: getId ) );
ones.addAll( collectionOfOnes ) ;

NavigableSet < TypeTwo > twos = new TreeSet <>( Comparator.comparingInt( TypeTwo :: getId ) );
twos.addAll( collectionOfTwos ) ;

Loop one navigable set while searching for a match in the other.

for( TypeOne one : ones )
{
    Optional<TypeTwo> optionalTwo = twos.stream().filter( two -> two.getId() == one.getId() ).findAny() ;
    // handle your Optional which may or may not contain an object. 
}
user_6427060
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