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Today I have released new video on "Find Perfect Number Using Java 8 Stream API | Interview Coding Question"This is frequently asked question in Java Interview.
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import java.util.List; import java.util.function.Predicate; import java.util.stream.Collectors; import java.util.stream.IntStream; public class FindPerfectNumber { public static void main(String[] args) { int sum = 0; int number = 28;
System.out.println("----------1. Using IntStream.rangeClosed() ---------------");
sum = IntStream.rangeClosed(1, number/2) .filter(i -> number % i == 0) .sum(); System.out.println(sum == number ? "Perfect Number" : "Not Perfect Number");
System.out.println("----------2. Using range() Instead of rangeClosed()---------");
sum = IntStream.range(1, number) .filter(i -> number % i == 0) .sum(); System.out.println(sum == number ? "Perfect Number" : "Not Perfect Number");
System.out.println("----------3. Using collection list and mapToInt---------"); List<Integer> divisors = IntStream.rangeClosed(1, number/2) .filter(i -> number % i == 0) .boxed() .collect(Collectors.toList());
sum = divisors.stream() .mapToInt(Integer::intValue) .sum(); System.out.println(sum == number ? "Perfect Number" : "Not Perfect Number");
System.out.println("----------4. Using reduce() method---------"); sum = IntStream.rangeClosed(1, number/2) .filter(i -> number % i == 0) .reduce(0, Integer::sum); System.out.println(sum == number ? "Perfect Number" : "Not Perfect Number");
System.out.println("----------5. Using One-Line Stream Solution---------"); boolean perfect = IntStream.rangeClosed(1, number/2) .filter(i -> number % i == 0) .sum() == number; System.out.println(perfect ? "Perfect Number" : "Not Perfect Number");
System.out.println("----------6. Using map() method---------"); sum = IntStream.rangeClosed(1, number/2) .filter(i -> number % i == 0) .map(i -> i) .sum(); System.out.println(perfect ? "Perfect Number" : "Not Perfect Number");
System.out.println("----------7. Using Predicate Function---------"); Predicate<Integer> divisorPred = i -> number % i == 0; sum = IntStream.rangeClosed(1, number/2) .filter(divisorPred :: test) .sum(); System.out.println(perfect ? "Perfect Number" : "Not Perfect Number");
System.out.println("----------8. Using peek() method for Debugging purpose---------"); sum = IntStream.rangeClosed( 1, number/2) .filter(i -> number % i == 0) .peek(i -> System.out.println(i)) .sum(); System.out.println(perfect ? "Perfect Number" : "Not Perfect Number");
} } output: ----------1. Using IntStream.rangeClosed() --------------- Perfect Number ----------2. Using range() Instead of rangeClosed()--------- Perfect Number ----------3. Using collection list and mapToInt--------- Perfect Number ----------4. Using reduce() method--------- Perfect Number ----------5. Using One-Line Stream Solution--------- Perfect Number ----------6. Using map() method--------- Perfect Number ----------7. Using Predicate Function--------- Perfect Number ----------8. Using peek() method for Debugging purpose--------- 1 2 4 7 14 Perfect Number |
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