Top 20 Java 8 Programming Interview Questions
6 min readMay 14, 2024
1- Write a Java Program to find whether a number is prime or not.
import java.util.stream.IntStream;//Prime numbers are natural numbers that are divisible by only 1 and the number itself
public class FindPrimeNumber { public static void main(String[] args) {
System.out.println(" Is Prime No : " + isPrimeByJava8(7));
}
private static boolean isPrimeByJava8(int n) {
if (n == 0 || n == 1) {
return false;
}
if (n == 2) {
return true;
}
boolean isPrime = IntStream.rangeClosed(2, n / 2).noneMatch(x -> n % x == 0);
return isPrime;
}
}
2-Write a Java Program to check Armstrong numbers.
//Armstrong number is the number in any given number base, which forms the total of the same number,
//when each of its digits is raised to the power of the number of digits in the number.
public class FindArmstrongNumber { public static void main(String[] args) {
System.out.println("Is Armstrong Number : " + isArmstrongNumberByJava8(371));
}
private static boolean isArmstrongNumberByJava8(int n) {
int len = String.valueOf(n).length();
int sum = String.valueOf(n).chars().map(ch -> Character.digit(ch, 10))
.map(digit -> (int) Math.pow(digit, len))
.sum();
return sum == n;
}
}3- Write a program to print duplicate numbers.
public class FindDuplicateNumber {public static void main(String[] args) {
int a[] = { 1, 4, 5, 2, 12, 34, 2, 11 };
System.out.println("Duplicate number by java 1.8 : " + findDuplicateNumberByJava1_8(a));
}
private static int findDuplicateNumberByJava1_8(int[] a) {
Map<Integer, Long> map = Arrays.stream(a).boxed()
.collect(Collectors.groupingBy(Function.identity(), Collectors.counting())); int duplicate = map.keySet().stream().filter(x -> map.get(x) > 1).findFirst().orElse(0); // If there have more then one duplicate then used this
map.keySet().stream().filter(x -> map.get(x) > 1).forEach(System.out::println);
return duplicate;
}
}
4-Write a program to find whether a string or number is palindrome or not.
//A Palindromic number is a number (such as 16461) that
// remains the same when its digits are reversed.
public class FindPalindromeNumber {
public static void main(String[] args) {
System.out.println(" Is Palindrome No : " + isPalindromeNumberByJava8(16461));
} private static boolean isPalindromeNumberByJava8(int n) {
String value = String.valueOf(n);
int len = value.length();
boolean isPalindromeNumber = IntStream.range(0, len / 2)
.anyMatch(index -> value.charAt(index) == value.charAt(len - index - 1));
return isPalindromeNumber;
}
}5- Write a program to print duplicate strings.
public class FindDuplicateInString {public static void main(String[] args) {
String input = "JavaAPI"; List<Character> duplicateList= input.chars().mapToObj(x -> Character.toUpperCase((char) x))
.collect(Collectors.groupingBy(Function.identity(), LinkedHashMap::new, Collectors.counting()))
.entrySet().stream().filter(x -> x.getValue() > 1L).map(Entry::getKey).collect(Collectors.toList()); System.out.println(duplicateListj);
}
}
6- Write a program to print the Fibonacci Series.
//The Fibonacci series is the sequence of numbers,
// where every number is the sum of the preceding two numbers.
public class FindFibonacciSeries {public static void main(String[] args) {
findFibonacciSeriesByJava8();
} private static void findFibonacciSeriesByJava8() {
Stream.iterate(new int[] { 0, 1 }, f -> new int[] { f[1], f[0] + f[1] }).limit(10).map(f -> f[0])
.forEach(System.out::println);
}
}
7- Write a program to find min and max numbers in the array.
public class FindMinAndMaxInArray {public static void main(String[] args) { int a[] = { 2, 3, 1, 22, 11, 33, 5 };// Find the max number
int max = Arrays.stream(a).boxed().max(Integer::compareTo).get(); System.out.println("Max Value by java 8 : "+max);
findMaxValue(a); // Find the min number
int min = Arrays.stream(a).boxed().max(Comparator.reverseOrder()).get(); System.out.println("Min Value by java 8 : "+min);
findMinValue(a); }
}
8-Write a program to find Min And Max In an Array Without using the max function
public class FindMinAndMaxInArrayWithoutMaxFunction {
public static void main(String[] args) {
int arr[] = { 2, 3, 1, 22, 11, 33, 5 };
int max = Arrays.stream(arr).boxed().reduce(Integer.MIN_VALUE, (a, b) -> Integer.max(a, b)).intValue();
int min = Arrays.stream(arr).boxed().reduce(Integer.MAX_VALUE, (a, b) -> Integer.min(a, b)).intValue();
System.out.println("Max : " + max + " Min : " + min); System.out.println();
// Using the method reference;
int max1 = Arrays.stream(arr).boxed().reduce(Integer::max).get();
int min1 = Arrays.stream(arr).boxed().reduce(Integer::min).get();
System.out.println("Max : " + max1 + " Min : " + min1);
}
}9-Write a program to find the second-highest number in an array.
public class FindSecondHighehestNumber {public static void main(String[] args) {
int a[] = { 3, 6, 32, 1, 8, 5, 31, 22 }; int secundMax = Arrays.stream(a).boxed().sorted(Comparator.reverseOrder()).skip(1).findAny().get();
System.out.println(secundMax);
}
}
10- Write a program to Find the Second Lowest Number.
public class FindSecondLowestNumber { public static void main(String[] args) {
int a[] = { 3, 6, 32, 1, 8, 5, 31, 22, 2 };
int secundMin = Arrays.stream(a).boxed().sorted().skip(1).findAny().get();
System.out.println(secundMin);
}
}11- Write a program to print the First Not Repeated Char in string.
public class FirstNotRepetedChar {public static void main(String[] args) {
String input = "Java Stream API is very good concept"; char firstNotRepetedChar = input.chars().mapToObj(x -> Character.toUpperCase((char) x))//converting the object format
.collect(Collectors.groupingBy(Function.identity(), LinkedHashMap::new, Collectors.counting()))// find duplicate freq in linkedHashMap
.entrySet().stream().filter(x -> x.getValue() == 1L).map(x -> x.getKey()).findFirst().get();//filtering the freq which is not first time System.out.println("First non repeated char : " + firstNotRepetedChar); }
}
12- Write a program to a Flattering list of objects.
public class FlatteringList {public static void main(String[] args) {
List<Integer> oddList = Arrays.asList(1, 3, 5, 7, 9, 11);
List<Integer> evenList = Arrays.asList(2, 4, 6, 8, 10);
List<List<Integer>> listOfList = Arrays.asList(oddList, evenList);
System.out.println(listOfList);
List<Integer> flatList = listOfList.stream().flatMap(list -> list.stream()).collect(Collectors.toList()); System.out.println(flatList);
}
}
13- Write a program to find the majority element in an array.
///Find the majority element in the array. A majority element in an array A[] of size n is
// an element that appears more than n/2 times.
public class MajorityElementInStream {public static void main(String[] args) {
int majorityArray[] = { 5, 3, 2, 1, 2, 4, 3, 2, 2, 6, 2, 3, 2, 2, 2 };
int notMajorityArray[] = { 3, 6, 32, 1, 8, 5, 31, 22 };
printMajorityElementByJava8(majorityArray);
printMajorityElementByJava8(notMajorityArray);
} private static void printMajorityElementByJava8(int a[]) {
int majorityElement = Arrays.stream(a).boxed()
.collect(Collectors.groupingBy(Function.identity(), HashMap::new, Collectors.counting())).entrySet()
.stream().filter(k -> k.getValue() >= a.length / 2).map(Entry::getKey).findFirst().orElse(0);
System.out.println(majorityElement);
}
}
14- Write a program to Print Even and Odd Numbers.
public class PrintEvenOddNumber {public static void main(String[] args) { printEvenNumberByJava8();
printOddNumberByJava8(); } private static void printEvenNumberByJava8() { IntStream.rangeClosed(0, 10).filter(x -> x % 2 == 0).forEach(System.out::println); } private static void printOddNumberByJava8() { IntStream.rangeClosed(0, 10).filter(x -> x % 2 != 0).forEach(System.out::println); }
}
15- Write a program to sort the 2 arrays in ascending order.
public class Sort2ArrayInAssendingOrder { public static void main(String[] args) {
int i[] = { 4, 5, 13, 22 };
int j[] = { 0, 9, 3, 7, 12, 11 };
List<Integer> sortedList= Stream.concat(Arrays.stream(i).boxed(), Arrays.stream(j).boxed()).sorted()
.collect(Collectors.toList());
System.out.println(sortedList);
}
}16-Write a program to sort the array.
public class SortArrayInReverseOrder {public static void main(String[] args) {
int a[] = { 3, 6, 32, 1, 8, 5, 31, 22 }; List<Integer> newArra = Arrays.stream(a).boxed().sorted().collect(Collectors.toList()); System.out.println(newArra); Arrays.sort(a);
System.out.println(Arrays.toString(a));
}
}
17-Write a program to sum an array.
public class SumArray { public static void main(String[] args) {
int a[] = { 3, 6, 32, 1, 8, 5, 31, 22 };
int sumValue = Arrays.stream(a).boxed().collect(Collectors.summingInt(Integer::intValue));
System.out.println(sumValue);
}
}18-Write a program to sum an array without using the sum method.
public class SumArray { public static void main(String[] args) {
int a[] = { 3, 6, 32, 1, 8, 5, 31, 22 };
int sum = Arrays.stream(a).boxed().reduce(0, (x, y) -> x + y).intValue();
System.out.println(sum);
}
}19- Write a program to append char in char ex-input- {A, B, C} output->[A_X, B_Y, C_Z].
public class AppendCharInChar { public static void main(String[] args) {
Stream<Character> charStream = Stream.of('A', 'B', 'C');
charStream.forEach(ch -> {
char newChar = (char) (ch + 23);
System.out.println(ch + "_" + newChar);
});
}
}20-Write a program to find the only duplicate count list in the List.
public class PrintOnlyDuplicateCountList {
public static void main(String[] args) {
List<String> names = Arrays.asList("Java", "Spring", "JPA", "Java", "Cloud", "JPA");
Map<String, Long> namesCount = names.stream().filter(x -> Collections.frequency(names, x) > 1)
.collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
System.out.println(namesCount);
}
}
