meet it

turns a stream of lines into a stream of words.

sorted() puts items in their natural order, or pass a comparator: sorted(Comparator.reverseOrder()). drops repeats. lets only the first three through, and skip(3) jumps past them. Together they make a top-three list in one pipeline.

Sometimes each item holds many values, like a line holding words. map would give a stream of arrays. flatMap opens each one up and pours the contents into a single stream: flatMap(line -> Arrays.stream(line.split(" "))).

A stream can be used once. After its terminal operation it is spent, and touching it again throws IllegalStateException. Need the data twice? Call stream() again.

import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;
public class Main {
    public static void main(String[] args) {
        List<String> lines = List.of("the cat sat", "on the mat", "the end");
        List<String> words = lines.stream()
            .flatMap(line -> Arrays.stream(line.split(" ")))
            .distinct()
            .sorted()
            .collect(Collectors.toList());
        System.out.println(words);
        List<Integer> top = List.of(40, 95, 70, 95, 12).stream()
            .sorted(Comparator.reverseOrder())
            .limit(3)
            .collect(Collectors.toList());
        System.out.println(top);
    }
}

Arrays.stream(array) opens a stream over an array, the way stream() does for a list.

guess first

`limit` first, `sorted` second. What will this show?

Guess before you run it. Wrong guesses are how you learn, and nothing is marked.

import java.util.List;
import java.util.stream.Collectors;
public class Main {
    public static void main(String[] args) {
        List<Integer> times = List.of(58, 41, 63, 39, 47);
        System.out.println(times.stream()
            .limit(3)
            .sorted()
            .collect(Collectors.toList()));
    }
}

your turn

Your turn. Gather every tag.

Each post holds a list of tags. On line 10, use flatMap to pour every post's tags into one stream. A list's stream() method gives a stream of its items.

Your code

output

press run to see what happens

fix it

The queue counts once, then crashes. Can you fix it?

Broken code to fix

output

press run to see what happens

The count works, then line 9 throws IllegalStateException. What happened to people on line 8?
count is a terminal operation, so the stream in people is spent after line 8.
Use a fresh stream each time: write queue.stream() in place of people on lines 8 and 9, then run.

nailed it

you can sort, slice and flatten streams. :D

sorted, distinct and limit run in the order you write them.
flatMap pours nested values into one flat stream.
A stream is used once. Call stream() again for more.

new words in your collection

distinct
limit
flatMap

This lesson isn’t saved. A free account remembers every lesson you finish.

flatMap turns a stream of lines into a stream of words.

limit first, sorted second. What will this show?

Your turn. Gather every tag.

The queue counts once, then crashes. Can you fix it?

you can sort, slice and flatten streams. :D

turns a stream of lines into a stream of words.

`limit` first, `sorted` second. What will this show?