Contents
hide
Introduction
A stream is like a pipeline with start, intermediate, and terminal operations, although it is similar to a Collection, however, there are some differences
- Stream does not store data
- Stream does not change the data source
- Stream is by default lazy
Write 5 Stream Sources
- Stream.of(“red”, “blue”, “green”, “black”);
- Stream.generate(Math::random);
- list.stream()
- Arrays.stream(array)
- IntStream.range(1, 3);
Convert a List of Strings(India, Canada, USA) to a List Of Characters
public class FlatMap {
public static void main(String[] args) {
List<String> words = Arrays.asList(new String[]{"India", "Canada", "USA"});
Stream<Stream<Character>> result1 = words.stream().map(w -> characterStream(w));
result1.forEach(System.out::println);
Stream<Character> result2 = words.stream().flatMap(w -> characterStream(w));
result2.forEach(System.out::println);
}
public static Stream<Character> characterStream(String s) {
List<Character> result = new ArrayList<>();
for (char c : s.toCharArray()) result.add(c);
return result.stream();
}
}
Finding the largest Element without using Built In Function from 4,8,24,3,22
private static void reduce() {
Optional<Integer> optional = Stream.of(4,8,24,3,22).reduce((i1, i2) -> i1 > i2 ? i1: i2);
System.out.println(optional.get());
}
Find the sum of the Words length – India, Canada, USA
private static void combinerAndAccumulator() {
Stream<String> strings = Stream.of("India", "Canada", "USA");
int result = strings.reduce(0, (x , y) -> x + y.length(), (x, y) -> x + y);
System.out.println(" Total SUM " + result);
}
Partition the List of Employees by Salary > x, Employee = id, name, salary
private static void partitionByDemo() {
Employee e1 = new Employee(1, "Jones", 1000);
Employee e2 = new Employee(2, "Smith", 1200);
Employee e3 = new Employee(3, "Adam", 1000);
Employee e4 = new Employee(4, "Chris", 1100);
Employee e5 = new Employee(5, "Dave", 1200);
List<Employee> employees = Arrays.asList(e1, e2, e3, e4, e5);
Map<Boolean, List<Employee>> employees1 = employees.stream().collect(Collectors.partitioningBy(x -> x.getSalary() > 1000));
System.out.println(employees1);
}
Group a List of Employees by Salary and name -> Employee = id, name, salary
public class Grouping {
public static void main(String[] args) {
groupingByDemo();
}
private static void groupingByDemo() {
Employee e1 = new Employee(1, "Jones", 1000);
Employee e2 = new Employee(2, "Smith", 1200);
Employee e3 = new Employee(3, "Adam", 1000);
Employee e4 = new Employee(4, "Chris", 1100);
Employee e5 = new Employee(5, "Dave", 1200);
List<Employee> employees = Arrays.asList(e1, e2, e3, e4, e5);
Map<Integer, List<String>> groupBySalary = employees.stream()
.collect(Collectors.groupingBy(x -> x.salary, Collectors.mapping(Employee::getName, Collectors.toList() )));
System.out.println(groupBySalary);
}
}
