Java 8 Coding Programs

Remove the duplicate elements from a list

List<String> list = Arrays.asList("Java", "C", "Python", "C", "Java", "Go");

List<String> distinctList = list.stream()
			   .distinct()
			   .collect(Collectors.toList());

System.out.println(distinctList);
//Output -> [Java, C, Python, Go]

Note – distinct() method returns a stream consisting of the distinct elements (according to Object.equals(Object)) of this stream.

Find duplicate elements in a list

Method -1

List<Integer> list = Arrays.asList(2,10,2,5,15,10,2);
	
Set<Integer> set = new HashSet<>();
Set<Integer> duplicates = list.stream()
				.filter(num -> !set.add(num))
				.collect(Collectors.toSet());
				
System.out.println(duplicates);
//Output - [2,10]

Method – 2

List<Integer> list = Arrays.asList(2,10,2,5,15,10,2);
    
Set<Integer> duplicates = list.stream()
				.filter(num -> Collections.frequency(list, num) > 1)
				.collect(Collectors.toSet());
		
System.out.println(duplicates);
//Output - [2,10]

Find the frequency of each element in a list

List<Integer> list = Arrays.asList(1, 3,5,1,4,3);

Map<Integer, Long> countMap = list.stream()
				.collect(Collectors.groupingBy(Function.identity(), 
                       Collectors.counting()));

System.out.println(countMap);
//Output -> 1=2, 3=2, 4=1, 5=1}

Find the frequency of each character in a string

String str = "Programming";
		
Map<Character, Long> countMap = str.chars()
        .mapToObj(ch -> (char) ch)
        .collect(Collectors.groupingBy(Function.identity(),
                          Collectors.counting()));
                          
System.out.println(countMap); 
//Output -> {P=1, a=1, r=2, g=2, i=1, m=2, n=1, o=1}

Find the second largest number in an integer list

List<Integer> list = Arrays.asList(2,10,2,5,15,10,2);
		
int secLargest = list.stream()
				.distinct()
				.sorted(Collections.reverseOrder())
				.skip(1)
				.findFirst()
				.get();

System.out.println(secLargest);
//Output -> 10

Find the second smallest number in an integer list

ListList<Integer> list = Arrays.asList(2,10,2,5,15,10,2);
		
int secSmallest = list.stream()
				.distinct()
				.sorted()
				.skip(1)
				.findFirst()
				.get();

System.out.println(secSmallest);
//Output -> 2

Find maximum 3 numbers in an integer list

List<Integer> list = Arrays.asList(2,10,2,5,15,10,2);

List<Integer> max3 = list.stream()
				.distinct()
				.sorted(Comparator.reverseOrder())
				.limit(3)
				.collect(Collectors.toList());

System.out.println(max3);
//Output -> [15, 10, 5]

Find minimum 3 numbers in an integer list

List<Integer> list = Arrays.asList(2,10,2,5,15,10,2);

List<Integer> min3 = list.stream()
				.distinct()
				.sorted()
				.limit(3)
				.collect(Collectors.toList());

System.out.println(min3);
//Output -> [2, 5, 10]