Java Concurrent

1. Synchronized & wait/notify/notifyAll used for communication between threads. (Random selected by JVM)

ReentrantLock & Condition can also do (selective选择性通知)
lock.lock() used to get the lock.
lock.unlock() used to release the lock

condition.await() // put current thread to Waiting status
condition.signal()

2. Executor, ExecutorService, ThreadPoolExecutor & Executors
Executor: An object that executes submitted Runnable tasks.
void execute(Runnable r)
ExecutorService: An Executor that provides methods to manage termination and methods that can produce a Future for tracking progress of one or more asynchronous tasks.