Java Lambda Streams — Free Java Tutorial

TL;DR: Learn Java Lambda Streams in Java with a free, beginner-friendly tutorial, examples and practice for Indian students on Syllab.in.

Java Lambda Streams in Java

Lambda expressions (Java 8+) are anonymous functions: (params) -> expression. They can be passed around as values and implement functional interfaces (interfaces with one abstract method).

Common functional interfaces: Predicate<T> (boolean test), Function<T,R> (T to R), Consumer<T> (accepts T, returns void), Supplier<T> (returns T), Comparator<T>.

The Stream API processes collections with a pipeline of operations: filter(), map(), sorted(), reduce(), collect(), count(), anyMatch(), findFirst().

Streams are lazy — intermediate operations (filter, map) don't execute until a terminal operation (collect, count, forEach) is called. This enables optimisation.

// Lambda syntax
Predicate<Integer> isEven = n -> n % 2 == 0;
Function<String, Integer> length = s -> s.length();
Comparator<String> byLength = (a, b) -> a.length() - b.length();

// Stream pipeline
list.stream()
    .filter(s -> s.marks >= 60)     // intermediate
    .map(s -> s.name)              

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