☕ JavaJava 8 Features

Stream API in Java 8

The Stream API completely changed how Java developers work with collections. Instead of writing for loops and if statements to filter, transform, and aggregate data, you chain descriptive operations. It reads like a SQL query, runs efficiently, and handles parallelism for free.

What is a Stream?

A Stream is a pipeline for processing a sequence of elements. It's NOT a data structure — it doesn't store data. It processes data from a source (collection, array, file) through a series of operations and produces a result. Two types of operations: • Intermediate — transform or filter the stream and return a new stream. Lazy — don't execute until a terminal operation triggers them. Examples: filter(), map(), sorted(), distinct(), limit() • Terminal — trigger execution and produce a result. Examples: collect(), forEach(), count(), reduce(), findFirst() Key insight: Streams are lazy. Nothing runs until you call a terminal operation. This allows Java to optimize the pipeline under the hood.

Stream Operations — Practical Examples

Java

import java.util.*;
import java.util.stream.*;

List<String> employees = Arrays.asList(
    "Alice-Engineering", "Bob-Marketing", "Charlie-Engineering",
    "Diana-HR", "Eve-Engineering"
);

// filter — keep only Engineering employees
List<String> engineers = employees.stream()
    .filter(e -> e.contains("Engineering"))
    .collect(Collectors.toList());
// [Alice-Engineering, Charlie-Engineering, Eve-Engineering]

// map — extract just the names
List<String> names = employees.stream()
    .map(e -> e.split("-")[0])   // take part before "-"
    .collect(Collectors.toList());
// [Alice, Bob, Charlie, Diana, Eve]

// sorted + distinct
List<Integer> scores = Arrays.asList(85, 92, 85, 78, 92, 65);
List<Integer> uniqueSorted = scores.stream()
    .distinct()
    .sorted()
    .collect(Collectors.toList());
// [65, 78, 85, 92]

// reduce — aggregate to a single value
int total = scores.stream().reduce(0, Integer::sum);  // 497

// count — how many pass a filter
long highScorers = scores.stream().filter(s -> s >= 85).count();  // 4

// anyMatch / allMatch / noneMatch — boolean checks
boolean hasFailure = scores.stream().anyMatch(s -> s < 60);  // false

Stream API in Java 8

What is a Stream?

Stream Operations — Practical Examples

Related Topics in Java 8 Features