🧠 1. Find Even Numbers using Stream

List<Integer> list = Arrays.asList(1,2,3,4,5,6);
list.stream().filter(n -> n % 2 == 0).forEach(System.out::println);

🧠 2. Convert List to Uppercase

List<String> names = Arrays.asList("java","python");
names.stream().map(String::toUpperCase).forEach(System.out::println);

🧠 3. Find Duplicate Elements

List<Integer> list = Arrays.asList(1,2,3,2,4,1);
Set<Integer> set = new HashSet<>();
list.stream().filter(n -> !set.add(n)).forEach(System.out::println);

🧠 4. Count Frequency using HashMap

String str = "java";
Map<Character,Integer> map = new HashMap<>();
for(char c : str.toCharArray()){
    map.put(c, map.getOrDefault(c,0)+1);
}
System.out.println(map);

🧠 5. Sort List using Lambda

List<Integer> list = Arrays.asList(5,2,8,1);
list.sort((a,b) -> a - b);
System.out.println(list);

🧠 6. Find Max Number using Stream

List<Integer> list = Arrays.asList(1,5,3,9);
int max = list.stream().max(Integer::compare).get();
System.out.println(max);

🧠 7. Find First Non-Repeating Character

String str = "aabbcde";
Map<Character,Long> map = str.chars()
    .mapToObj(c -> (char)c)
    .collect(Collectors.groupingBy(c -> c, LinkedHashMap::new, Collectors.counting()));

map.entrySet().stream()
    .filter(e -> e.getValue() == 1)
    .findFirst()
    .ifPresent(System.out::println);

🧠 8. Reverse String using Stream

String str = "hello";
String rev = new StringBuilder(str).reverse().toString();
System.out.println(rev);

🧠 9. Remove Duplicates from List

List<Integer> list = Arrays.asList(1,2,2,3);
list.stream().distinct().forEach(System.out::println);

🧠 10. Sum of Numbers using Stream

int sum = Arrays.asList(1,2,3,4).stream().mapToInt(i -> i).sum();
System.out.println(sum);

🧠 11. Group Strings by Length

List<String> list = Arrays.asList("hi","hello","hey");
Map<Integer,List<String>> map = list.stream()
    .collect(Collectors.groupingBy(String::length));
System.out.println(map);

🧠 12. Check Palindrome using Lambda

String str = "madam";
boolean isPal = str.equals(new StringBuilder(str).reverse().toString());
System.out.println(isPal);

🧠 13. Functional Interface Example

@FunctionalInterface
interface Test {
    void show();
}

Test t = () -> System.out.println("Hello");
t.show();

🧠 14. Sort Map by Value

Map<String,Integer> map = new HashMap<>();
map.put("A",3); map.put("B",1);

map.entrySet().stream()
    .sorted(Map.Entry.comparingByValue())
    .forEach(System.out::println);

🧠 15. Count Words in Sentence

String str = "java is java";
Map<String,Long> map = Arrays.stream(str.split(" "))
    .collect(Collectors.groupingBy(w -> w, Collectors.counting()));
System.out.println(map);

🧠 16. Find Second Highest Number

List<Integer> list = Arrays.asList(1,5,8,3);
int second = list.stream().sorted(Collections.reverseOrder()).skip(1).findFirst().get();
System.out.println(second);

🧠 17. Merge Two Lists

List<Integer> l1 = Arrays.asList(1,2);
List<Integer> l2 = Arrays.asList(3,4);
List<Integer> merged = Stream.concat(l1.stream(), l2.stream()).collect(Collectors.toList());
System.out.println(merged);

🧠 18. Convert List to Map

List<String> list = Arrays.asList("A","B");
Map<String,Integer> map = list.stream()
    .collect(Collectors.toMap(s -> s, String::length));
System.out.println(map);

🧠 19. Find Longest String

List<String> list = Arrays.asList("java","spring","boot");
String longest = list.stream().max(Comparator.comparing(String::length)).get();
System.out.println(longest);

🧠 20. Filter Null Values

List<String> list = Arrays.asList("a",null,"b");
list.stream().filter(Objects::nonNull).forEach(System.out::println);

🧠 21. HashSet Example (Unique Elements)

Set<Integer> set = new HashSet<>(Arrays.asList(1,2,2,3));
System.out.println(set);

🧠 22. Find Intersection of Two Lists

List<Integer> l1 = Arrays.asList(1,2,3);
List<Integer> l2 = Arrays.asList(2,3,4);
l1.stream().filter(l2::contains).forEach(System.out::println);

🧠 23. Count Characters using Stream

String str = "hello";
Map<Character,Long> map = str.chars()
    .mapToObj(c -> (char)c)
    .collect(Collectors.groupingBy(c -> c, Collectors.counting()));
System.out.println(map);

🧠 24. Sort Strings Alphabetically

List<String> list = Arrays.asList("banana","apple");
list.stream().sorted().forEach(System.out::println);

🧠 25. Find Any Element using Stream

List<Integer> list = Arrays.asList(1,2,3);
list.stream().findAny().ifPresent(System.out::println);