Intermediate Operations

Common Intermediate Operations

Operation	What it does
`filter(Predicate)`	keep matching elements
`map(Function)`	transform each element
`mapToInt / mapToObj`	switch between object and primitive streams
`flatMap(Function)`	one element → many, flattened
`distinct()`	remove duplicates (uses equals)
`sorted()`, `sorted(Comparator)`	sort
`limit(n)`, `skip(n)`	take first n / skip first n (pagination)
`takeWhile / dropWhile` (Java 9)	take / drop while a condition holds
`peek(Consumer)`	look at elements (debugging only)
`mapMulti` (Java 16)	imperative alternative to flatMap

Products Page Pipeline

Example

Page 2 of in-stock products (2 per page), sorted by price.

import java.util.*;

public class Main {
    public static void main(String[] args) {
        List<Product> products = List.of(
                new Product("Phone", 15999, 5), new Product("Cover", 299, 0),
                new Product("Charger", 899, 12), new Product("Earbuds", 1999, 3),
                new Product("Cable", 199, 40), new Product("Phone", 15999, 5));

        int page = 2, size = 2;
        List<String> pageItems = products.stream()
                .distinct()
                .filter(p -> p.stock() > 0)
                .sorted(Comparator.comparingInt(Product::price))
                .skip((long) (page - 1) * size)
                .limit(size)
                .map(p -> p.name() + " Rs" + p.price())
                .toList();
        System.out.println(pageItems);

        List<Integer> temps = List.of(28, 30, 33, 36, 31, 29);
        System.out.println("takeWhile < 35: " + temps.stream().takeWhile(t -> t < 35).toList());
        System.out.println("dropWhile < 35: " + temps.stream().dropWhile(t -> t < 35).toList());
    }
}

record Product(String name, int price, int stock) {}

Output

[Earbuds Rs1999, Phone Rs15999]
takeWhile < 35: [28, 30, 33]
dropWhile < 35: [36, 31, 29]

Practice

Exercise: From List.of(5, 3, 5, 1, 3, 8) get the distinct numbers in descending order.

Show answer

List<Integer> r = List.of(5, 3, 5, 1, 3, 8).stream()
        .distinct()
        .sorted(Comparator.reverseOrder())
        .toList();
System.out.println(r); // [8, 5, 3, 1]