Java Multithreading - Quick Revision for Interviews || The Ultimate Interview Guide | Java In Action

Introduction & Basics (0:00)
Multithreading is introduced as the core concept enabling modern software to handle many tasks simultaneously (0:00-0:45).
A Thread is defined as the smallest unit of work an OS can manage (0:48-2:25). Threads within the same process share memory.
The video differentiates between CPU-bound tasks (heavy processing) and I/O-bound tasks (waiting for data), explaining when multithreading is most beneficial (3:34-4:03).

Thread Creation (7:42)
Four ways to create threads are discussed.
Extending `Thread` (8:30-9:42) is presented as a legacy approach due to Java's single inheritance.
Implementing `Runnable` (9:45-11:15) is highlighted as a better practice, decoupling the task from the thread.
`Callable` & `Future` (11:16-12:08) are introduced for tasks that return a result or throw exceptions.
`ExecutorService` (12:09-12:59, 14:34-15:13) is emphasized as the modern best practice for managing thread pools and improving performance.
An interview question clarifies the difference between `start()` (initiates a new thread) and `run()` (executes on the current thread) (13:02-13:59).

Thread Lifecycle (15:20)
Threads move through states: New, Runnable, and Terminated (16:35-18:17).
Waiting States include Blocked (waiting for a lock), Waiting (indefinitely waiting for a signal), and Timed_Waiting (waiting for a signal or timeout) (18:20-19:53).
A key interview distinction is made between `sleep()` (holds lock) and `wait()` (releases lock) (20:41-22:27).

Scheduling & Priority (23:36)
Thread scheduling is primarily managed by the Operating System, not solely the JVM (24:07-25:12).
Thread Priority is described as merely a "hint" or "suggestion," offering no guarantees of execution order (25:46-27:50).

Synchronization (29:45)
Synchronization is necessary to prevent race conditions and ensure mutual exclusion and visibility of shared data (31:18-33:05).
Synchronized blocks are preferred over synchronized methods for their precision and performance (33:06-34:10).
It's explicitly stated that you cannot synchronize a constructor because an object (and its lock) doesn't exist during construction (36:01-36:47).

Inter-Thread Communication (37:50)
Methods like `wait()`, `notify()`, and `notifyAll()` are used for thread coordination (39:18-40:58).
The video emphasizes using `wait()` inside a `while` loop to guard against "spurious wakeups" (41:03-41:56).

The Producer-Consumer Problem is presented as a classic example of inter-thread communication (44:59, 45:48-51:13).
The modern and safer solution for this problem is the `BlockingQueue` (50:48-51:13).

Concurrency Issues (52:19)
Deadlock is defined as a circular waiting condition where threads are permanently blocked (52:50-54:17).
Livelock involves threads actively changing states but making no progress (55:01-56:36).
Starvation refers to a thread being consistently denied access to resources (56:38-58:10).