We can identify duplicate elements in a Java Stream by making use of the Collectors.groupingBy collector with Collectors.counting.
Example:import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
public class Example {
public static void main(String[] args) {
List<Integer> numbers = Arrays.asList(1, 2, 2, 3, 3, 5, 4);
List<Integer> duplicates = numbers.stream()
.collect(Collectors.groupingBy(e -> e, Collectors.counting()))
.entrySet().stream()
.filter(entry -> entry.getValue() > 1)
.map(Map.Entry::getKey)
.collect(Collectors.toList());
System.out.println("Duplicate in " + numbers + " are : " + duplicates);
}
}
Output:
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