Java Collections & Concurrency¶
Master Java's collection framework, functional programming paradigm, concurrent utilities, and stream processing for efficient, thread-safe applications.
Topics¶
Collections¶
List - Set - Map - ArrayList - HashMap - HashSet - LinkedHashMap - TreeMap - ConcurrentHashMap
Collection framework: interface hierarchy, implementations, time complexity (access/insert/delete), when to use each, thread-safety, null handling, iteration patterns.
Functional Programming¶
Lambdas - Functional Interfaces - Method References - Function Composition - Higher-Order Functions
Functional paradigm in Java: lambda syntax, @FunctionalInterface, method references, function composition, common functional interfaces (Function, Predicate, Consumer, Supplier).
Streams¶
Stream API - Lazy Evaluation - Intermediate Operations - Terminal Operations - Collectors - Reduction
Stream processing: creating streams, filter/map/flatMap/reduce, collect operations, parallel streams, performance considerations, common patterns.
Concurrency & Threads¶
Thread Creation - Synchronization - Locks - Atomics - Volatile - Executors - Thread Pools - Future
Concurrent programming: thread lifecycle, race conditions, synchronization mechanisms, ReentrantLock, ConcurrentHashMap, thread pools, async patterns with Future/CompletableFuture.
Threading Deep-Dive & Virtual Threads¶
Thread Synchronization - Atomic Operations - Thread Pools - Virtual Threads (Java 21) - Structured Concurrency - Concurrency Patterns
Advanced threading: synchronized vs. locks, atomics without locking, ExecutorService, virtual threads for millions of concurrent tasks, comparison with reactive frameworks, producer-consumer and barrier patterns.
Testing¶
Unit Testing - Mocking - Test Collections - Concurrency Testing - Thread Safety Verification
Testing Java applications: JUnit, Mockito, testing collections, concurrent code testing, race condition detection, integration testing.
Quick Interview Prep¶
Collections mastery: - ArrayList O(1) access, O(n) insert/delete; LinkedList O(n) access, O(1) insert/delete - HashMap O(1) average, O(n) worst; TreeMap O(log n) all operations, sorted order - Thread-safe: ConcurrentHashMap, Collections.synchronizedList(), CopyOnWriteArrayList
Concurrency essentials: - synchronized keyword for methods/blocks; ReentrantLock for fine-grained control - volatile for visibility; AtomicInteger, AtomicReference for atomic operations - Thread pools: Executors.newFixedThreadPool(), newCachedThreadPool() - CompletableFuture for async chaining without callbacks
Streams patterns: - filter-map-collect for transformations - reduce() for aggregations - parallel() for multi-threaded processing (careful with side effects!)