StreamsAPI-Tutorials/StreamExamples/DistinctByKeys.java at main · CodeJamm/StreamsAPI-Tutorials · GitHub

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package StreamExamples;

import java.util.Arrays;

import java.util.List;

import java.util.Map;

import java.util.concurrent.ConcurrentHashMap;

import java.util.function.Function;

import java.util.function.Predicate;

import java.util.stream.Collectors;

import java.util.stream.Stream;

import StudentClass.Student;

public class DistinctByKeys

{

public static void main(String[] args)

{

Stream.of(new Student(1,"Ram"),new Student(2,"Arjun"),new Student(3,"Kavi"),new Student(4,"Sanju"),new Student(5,"Ajay"))

.filter(distinctByKeys(Student::getID, Student::getName))

.collect(Collectors.toList()).forEach(System.out::println);

System.out.println();

}

private static <T> Predicate<T> distinctByKeys(Function<? super T, ?>... keyExtractors)

{

final Map<List<?>, Boolean> seen = new ConcurrentHashMap<>();

return t ->

{

final List<?> keys = Arrays.stream(keyExtractors)

.map(ke -> ke.apply(t))

.collect(Collectors.toList());

return seen.putIfAbsent(keys, Boolean.TRUE) == null;

};

}

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