Java Cheatsheet
A quick-reference guide for working Java developers.
Collections
Lists, Sets, Maps, Queues — the non-concurrent collection classes, their trade-offs, and time complexities.
Concurrent Collections
Thread-safe collections from java.util.concurrent — ConcurrentHashMap, blocking queues, copy-on-write lists, and more.
Modern Java
Records, sealed interfaces, pattern matching, and lambdas — the features that make modern Java expressive.
Threading Primitives
synchronized, volatile, locks, conditions, and atomic classes — low-level concurrency building blocks.
Executors & Thread Pools
Thread pools, ExecutorService, Future, CompletableFuture — structured concurrency at a higher level.
Virtual Threads
Project Loom's lightweight threads — scalable concurrency without the complexity of reactive programming.
Spring Boot
Annotations, auto-configuration, dependency injection, REST controllers, data access, and testing essentials.