Functional Java: Master Java Lambdas and Streams

Explore how to type a lambda in Java by defining interface methods that specify argument count, order, and return type; use a single-method interface as a proxy to type lambdas.

Understand how a single abstract method in an interface defines the lambda signature, letting you assign a lambda to that interface type by matching its method inputs and return.

Use the functional interface annotation to enforce a single abstract method, catching errors when a second abstract method is added; lambdas work without it, but it communicates intent.

Define arity as the number of input arguments, classify nullary, unary, binary, and ternary functions, and show unary and binary coverage for by function, by consumer, and by predicate.

Explore method references in Java to replace simple lambdas, delegating work to static methods like Math.random, and use ClassName::methodName to keep IntelliJ happy.

Examine how closures capture scope in Java lambdas, remembering the value instead of the variable. Learn why variables used in lambdas must be final or effectively final.

Explore streams as a design pattern for processing elements in collections, offering an internal iteration model with lambdas and a reusable examine method.

Create a stream from a collection and apply operations with a forEach consumer, using a lambda or method reference to print each element.

Explore multiple ways to create streams beyond collections, including stream off and arrays stream, file lines, and generate or iterate patterns, while recognizing streams as independent processing lines.

Explore converting a stream to a list with the toList method by generating a range of numbers via iterate and limit, then collecting the first 100 elements.

Identify the three key elements of streams: the stream itself, intermediate operations, and terminal operations. Compare sequential and parallel streams, and note how terminal operations yield results or side effects.

Discover the peek operator in Java streams, enabling debugging by peeking into map and filter results with a consumer for side effects like printing, while returning a new stream.