Java 8 coding practice Q & A

kjkjkjkjk

Given a list of integers, find out all the even numbers that exist in the list using Stream functions?

import java.util.*;import java.util.stream.*;public class EvenNumber{    public static void main(String args[]) {      List<Integer> list = Arrays.asList(10,15,8,49,25,98,32);            list.stream()                .filter(n -> n%2 == 0)                .forEach(System.out::println);    /* or can also try below method */    Map<Boolean, List<Integer>> list = Arrays.stream(nums).boxed()    .collect(Collectors.partitioningBy(num -> num % 2 == 0));    System.out.println(list);       }   }Output: 10, 8, 98, 32

2. Given a list of integers, find out all the numbers starting with 1 using Stream functions?

import java.util.*;import java.util.stream.*;public class NumberStartingWithOne{    public static void main(String args[]) {            List<Integer> myList = Arrays.asList(10,15,8,49,25,98,32);            myList.stream()                  .map(s -> s + "") // Convert integer to String                  .filter(s -> s.startsWith("1"))                  .forEach(System.out::println);/* or can also try below method */      List<String> list = Arrays.stream(arr).boxed()                                .map(s -> s + "")                                .filter(s -> s.startsWith("1"))                                .collect(Collectors.toList());    System.out.println(list);    }}Output:10, 15

3. How to find duplicate elements in a given integers list in java using Stream functions?

import java.util.*;import java.util.stream.*;public class DuplicateElements {  public static void main(String args[]) {          List<Integer> myList = Arrays.asList(10,15,8,49,25,98,98,32,15);          Set<Integer> set = new HashSet();          myList.stream()                .filter(n -> !set.add(n))                .forEach(System.out::println);  }}Output:98, 15// Or you can also try using distinct() keywordpublic static void getDataWithoutDuplicates() {     List<Integer> myList = Arrays.asList(1, 1, 85, 6, 2, 3, 65, 6, 45, 45, 5662, 2582, 2, 2, 266, 666, 656);     myList.stream().distinct().forEach(noDuplicateData -> System.out.println(noDuplicateData)); }Output : 1 85 6 2 3 65 45 5662 2582 266 666 656//Or you can also use below public static void getDataWithoutDuplicates() {      List<Integer> myList = Arrays.asList(1, 1, 85, 6, 2, 3, 65, 6, 45, 45, 5662, 2582, 2, 2, 266, 666, 656);      Set<Integer> set = new HashSet<>(myList);              // Convert the set back to a list if needed      List<Integer> uniqueData = set.stream().collect(Collectors.toList());              // Print the unique elements      uniqueData.forEach(System.out::println);  }Output : 1 65 2 3 6 266 45 656 85 2582 666 5662/* or can also try below single line code */List<Integer> list = Arrays.stream(arr).boxed().distinct().collect(Collectors.toList());

4. Given the list of integers, find the first element of the list using Stream functions?

import java.util.*;import java.util.stream.*;public class FindFirstElement{  public static void main(String args[]) {          List<Integer> myList = Arrays.asList(10,15,8,49,25,98,98,32,15);          myList.stream()                .findFirst()                .ifPresent(System.out::println);      /* or can also try below single line code */      Arrays.stream(arr).boxed().findFirst().ifPresent(System.out::print);  }}Output:10

5. Given a list of integers, find the total number of elements present in the list using Stream functions?

import java.util.*;import java.util.stream.*;public class FindTheTotalNumberOfElements{  public static void main(String args[]) {          List<Integer> myList = Arrays.asList(10,15,8,49,25,98,98,32,15);          long count =  myList.stream()                              .count();          System.out.println(count);   /* or can also try below line code */      Arrays.stream(arr).boxed().count();               }}Output:9

6. Given a list of integers, find the maximum value element present in it using Stream functions?

import java.util.*;import java.util.stream.*;public class FindMaxElement{  public static void main(String args[]) {          List<Integer> myList = Arrays.asList(10,15,8,49,25,98,98,32,15);          int max =  myList.stream()                           .max(Integer::compare)                           .get();          System.out.println(max);   /* or we can try using below way */        int maxdata = Arrays.stream(arr).boxed()                            .max(Comparator.naturalOrder()).get();         System.out.println(maxdata);                }}Output:98

7. Given a String, find the first non-repeated character in it using Stream functions?

import java.util.*;import java.util.stream.*;import java.util.function.Function;public class FirstNonRepeated{  public static void main(String args[]) {    String input = "Java articles are Awesome";        Character result = input.chars() // Stream of String                   .mapToObj(s -> Character.toLowerCase(Character.valueOf((char) s))) // First convert to Character object and then to lowercase                     .collect(Collectors.groupingBy(Function.identity(), LinkedHashMap::new, Collectors.counting())) //Store the chars in map with count             .entrySet()            .stream()            .filter(entry -> entry.getValue() == 1L)            .map(entry -> entry.getKey())            .findFirst()            .get();    System.out.println(result);     /* or can also try using */        input.chars().mapToObj(c -> (char) c)               .filter(ch -> input.indexOf(ch) == input.lastIndexOf(ch))               .findFirst().orElse(null);                     }}Output:j

8. Given a String, find the first repeated character in it using Stream functions?

import java.util.*;import java.util.stream.*;import java.util.function.Function;public class FirstRepeated{  public static void main(String args[]) {          String input = "Java Articles are Awesome";          Character result = input.chars() // Stream of String                                         .mapToObj(s -> Character.toLowerCase(Character.valueOf((char) s))) // First convert to Character object and then to lowercase                                           .collect(Collectors.groupingBy(Function.identity(), LinkedHashMap::new, Collectors.counting())) //Store the chars in map with count                                   .entrySet()                                  .stream()                                  .filter(entry -> entry.getValue() > 1L)                                  .map(entry -> entry.getKey())                                  .findFirst()                                  .get();          System.out.println(result);        /* or can also try */        Set<Character> seenCharacters = new HashSet<>();        return input.chars()                    .mapToObj(c -> (char) c)                    .filter(c -> !seenCharacters.add(c))                    .findFirst()                    .orElse(null);                  }}  Output:a

9. Given a list of integers, sort all the values present in it using Stream functions?

import java.util.*;import java.util.stream.*;import java.util.function.Function;public class SortValues{  public static void main(String args[]) {          List<Integer> myList = Arrays.asList(10,15,8,49,25,98,98,32,15);           myList.stream()                 .sorted()                 .forEach(System.out::println);        /* Or can also try below way */        Arrays.stream(arr).boxed().sorted().collect(Collectors.toList())  }}Output: 81015152532499898

10. Given a list of integers, sort all the values present in it in descending order using Stream functions?

import java.util.*;import java.util.stream.*;import java.util.function.Function;public class SortDescending{  public static void main(String args[]) {          List<Integer> myList = Arrays.asList(10,15,8,49,25,98,98,32,15);           myList.stream()                 .sorted(Collections.reverseOrder())                 .forEach(System.out::println);  }}Output:98984932251515108

11. Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct.

public boolean containsDuplicate(int[] nums) {    List<Integer> list = Arrays.stream(nums)                               .boxed()                               .collect(Collectors.toList());    Set<Integer> set = new HashSet<>(list);     if(set.size() == list.size()) {       return false;   }       return true;/* or can also try below way */     Set<Integer> setData = new HashSet<>();        return Arrays.stream(nums)                     .anyMatch(num -> !setData.add(num));  }Input: nums = [1,2,3,1]Output: trueInput: nums = [1,2,3,4]Output: false

12. How will you get the current date and time using Java 8 Date and Time API?

class Java8 {    public static void main(String[] args) {        System.out.println("Current Local Date: " + java.time.LocalDate.now());        //Used LocalDate API to get the date        System.out.println("Current Local Time: " + java.time.LocalTime.now());        //Used LocalTime API to get the time        System.out.println("Current Local Date and Time: " + java.time.LocalDateTime.now());        //Used LocalDateTime API to get both date and time    }}

13. Write a Java 8 program to concatenate two Streams?

import java.util.Arrays;import java.util.List;import java.util.stream.Stream; public class Java8 {    public static void main(String[] args) {         List<String> list1 = Arrays.asList("Java", "8");        List<String> list2 = Arrays.asList("explained", "through", "programs");         Stream<String> concatStream = Stream.concat(list1.stream(), list2.stream());                 // Concatenated the list1 and list2 by converting them into Stream         concatStream.forEach(str -> System.out.print(str + " "));                 // Printed the Concatenated Stream             }}

14. Java 8 program to perform cube on list elements and filter numbers greater than 50.

import java.util.*;public class Main {    public static void main(String[] args) {       List<Integer> integerList = Arrays.asList(4,5,6,7,1,2,3);       integerList.stream()                  .map(i -> i*i*i)                  .filter(i -> i>50)                  .forEach(System.out::println);    }}  Output:64125216343

15. Write a Java 8 program to sort an array and then convert the sorted array into Stream?

import java.util.Arrays; public class Java8 {     public static void main(String[] args) {        int arr[] = { 99, 55, 203, 99, 4, 91 };        Arrays.parallelSort(arr);        // Sorted the Array using parallelSort()                 Arrays.stream(arr).forEach(n > System.out.print(n + " "));        /* Converted it into Stream and then           printed using forEach */    }}

16. How to use map to convert object into Uppercase in Java 8?

public class Java8 {     public static void main(String[] args) {        List<String> nameLst = names.stream()                                    .map(String::toUpperCase)                                    .collect(Collectors.toList());        System.out.println(nameLst);    }}output:AA, BB, CC, DD

17. How to convert a List of objects into a Map by considering duplicated keys and store them in sorted order?

public class TestNotes {    public static void main(String[] args) {    List<Notes> noteLst = new ArrayList<>();    noteLst.add(new Notes(1, "note1", 11));    noteLst.add(new Notes(2, "note2", 22));    noteLst.add(new Notes(3, "note3", 33));    noteLst.add(new Notes(4, "note4", 44));    noteLst.add(new Notes(5, "note5", 55));    noteLst.add(new Notes(6, "note4", 66));    Map<String, Long> notesRecords = noteLst.stream()                                            .sorted(Comparator                                            .comparingLong(Notes::getTagId)                                            .reversed()) // sorting is based on TagId 55,44,33,22,11                                            .collect(Collectors.toMap                                            (Notes::getTagName, Notes::getTagId,                                            (oldValue, newValue) -> oldValue,LinkedHashMap::new));// consider old value 44 for dupilcate key// it keeps order        System.out.println("Notes : " + notesRecords);    }}

18. How to count each element/word from the String ArrayList in Java8?

public class TestNotes {    public static void main(String[] args) {        List<String> names = Arrays.asList("AA", "BB", "AA", "CC");        Map<String,Long> namesCount = names                                .stream()                                .collect(                                 Collectors.groupingBy(                                  Function.identity(), Collectors.counting()));        System.out.println(namesCount);  }}Output:{CC=1, BB=1, AA=2}

19. How to find only duplicate elements with its count from the String ArrayList in Java8?

public class TestNotes {    public static void main(String[] args)       List<String> names = Arrays.asList("AA", "BB", "AA", "CC");      Map<String,Long> namesCount = names                                   .stream()                       .filter(x->Collections.frequency(names, x)>1)                       .collect(Collectors.groupingBy                       (Function.identity(), Collectors.counting()));      System.out.println(namesCount);/*or you can also try using  */Map<String, Long> namesCount = names.stream()                .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()))                .entrySet()                .stream()                .filter(entry -> entry.getValue() > 1)                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));  }}Output:{AA=2}

20. How to check if list is empty in Java 8 using Optional, if not null iterate through the list and print the object?

Optional.ofNullable(noteLst)            .orElseGet(Collections::emptyList) // creates empty immutable list: [] in case noteLst is null            .stream().filter(Objects::nonNull) //loop throgh each object and consider non null objects            .map(note -> Notes::getTagName) // method reference, consider only tag name            .forEach(System.out::println); // it will print tag names

21. Write a Program to find the Maximum element in an array?

public static int findMaxElement(int[] arr) {  return Arrays.stream(arr).max().getAsInt();}Input: 12,19,20,88,00,9output: 88

22. Write a program to print the count of each character in a String?

public static void findCountOfChars(String s) {Map<String, Long> map = Arrays.stream(s.split(""))                              .map(String::toLowerCase)                              .collect(Collectors                              .groupingBy(str -> str,                                 LinkedHashMap::new, Collectors.counting()));// or you can also try using Function.identify() instead of LinkedHashMapMap<String, Long> mapObject = Arrays.stream(s.split(""))                                    .map(String::toLowerCase)   .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));}Input: String s = "string data to count each character";Output: {s=1, t=5, r=3, i=1, n=2, g=1,  =5, d=1, a=5, o=2, c=4, u=1, e=2, h=2}