Summary - Stream API basics

Combine filter, map and collect to write an employee filter.

Summary - Stream API basics

This group covered the core Stream API operations: stream() starts the stream, filter removes elements, map transforms, forEach and count are terminal ops, collect(Collectors.toList()) gathers the result into a List.

Intermediate operations are lazy; terminal operations are eager. A Stream is consumed once; reusing it is an error. The Predicate, Function and Consumer functional interfaces are given as lambdas.

Exercise Stream chain: filter, map, collect

Declare List<String> names = new ArrayList<>();; add "Ayşe", "Alex", "Mehmet". Build the chain List<Integer> lengths = names.stream().filter(s -> s.length() > 3).map(s -> s.length()).collect(Collectors.toList());. Print the size with System.out.println(lengths.size());.

Show example solution

import java.util.List;
import java.util.ArrayList;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();
        names.add("Ayşe");
        names.add("Alex");
        names.add("Mehmet");
        List<Integer> lengths = names.stream().filter(s -> s.length() > 3).map(s -> s.length()).collect(Collectors.toList());
        System.out.println(lengths.size());
    }
}

Test yourself

Match the operation types

filter

Filtering (intermediate)
map

Transform (intermediate)
forEach

Side effect (terminal)
count

Counting (terminal)
Which one is a terminal operation?
- collect
- map
- filter
- sorted
Show answer

collect — collect is terminal; it gathers the stream into a List and closes it.
Match the Stream parts

stream()

Starts the stream
Collectors.toList()

Gathers a List
Predicate<T>

filter parameter
Function<T, R>

map parameter

Next lesson: Project design

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies