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Traditional multithreading in Java using Thread , Runnable , synchronized , and wait/notify works, but it becomes difficult to scale in modern backend applications. Java introduced the java.util.concurrent package to simplify concurrency, improve performance, and avoid common threading issues. 1. Why java.util.concurrent? Older threading models had several limitations: Manual thread creation → expensive & slow Risk of race conditions Complex synchronization No proper thread lifecycle management The concurrency framework solves these problems using: Thread pools Locks Atomic variables Coordination tools Asynchronous computation 2. ExecutorService (Thread Pooling) ExecutorService manages threads efficiently and avoids creating too many threads. ExecutorService service = Executors.newFixedThreadPool(5); service.submit(() -> System.out.println("Task executed")); Types of Executor Services: newSingleThreadExecutor() – ...

After understanding threads and multithreading basics, the next step in modern Java concurrency is learning how to manage threads efficiently. Manually creating threads is inefficient, difficult to control, and not scalable. Java solves these issues using ExecutorService, Future, and CompletableFuture. Why ExecutorService? ExecutorService provides a flexible framework for managing and reusing threads. It removes the need to manually create, start, and manage individual threads. Efficient resource utilization Thread reuse using thread pools Better performance Simpler asynchronous programming Avoids creating too many threads Types of Executor Services Java offers several ready-to-use executors based on usage: newSingleThreadExecutor: Executes tasks sequentially in one thread. newFixedThreadPool: Maintains a fixed number of threads. newCachedThreadPool: Creates threads as needed; good for short-lived tasks. newScheduledThreadPool: Executes delayed a...