Interview ready notes/points - Java Threads

• A thread is a single sequential flow of control within a process. A single process can thus have multiple concurrently executing threads.
• To run a thread call the start() method on the instance of the thread class.
• The thread's start() method registers the thread with "Thread Scheduler".
• The "Thread Scheduler" resides in Operating System and JVM.
• The thread's start() method puts the thread in ready state and makes the thread eligible to run.
• When the thread runs it executes run() method of a thread.
• A thread can execute it's own run() method or another objects run() method.
• If you call start() method of a thread , it automatically calls the run() method.
• If you extend your class to Thread class, you cannot extends to another class.
• There are two ways to create a thread class one way is by extending Thread class or by implementing Runnable interface.
• After completion of executing run() method a thread is considered to be a dead thread.
• You cannot start a dead thread, but variables and methods can be called.
• The interrupt() method forcibly puts the thread into dead state.
• If there are many threads are waiting then there is no guaranty that which thread is going to called by the "Thread Scheduler".
• The yield() method puts currently running thread in to ready state.
• The sleep() and yield() methods runs only on currently threads.
• If a sleeping thread receives interrupt() method call the thread immediately moves to ready state otherwise it throws an "InterruptedException".
• Sometimes it may true that a thread might be waiting for input or operation to be performed before it can continue, this kind of waiting of a thread said to thread become blocked or "Blocking State".
• A monitor is an object which contains some synchronized code in it.
• The keyword "synchronized" is used to mark entire method or block of code as synchronized.
• The java.lang.Object class methods wait(), notify() and notifyAll() will be called from only in "synchronized" code. These methods are used in thread communications.
• If you call wait() method on a thread it releases CPU, releases objects lock, the thread enters into pool of waiting threads.
• Calling notify() method the waiting thread moves out of the waiting pool to ready state , but there is no guaranty which thread will be moved out of the pool.
• Calling notifyAll() moves all waiting threads will be moved out of the waiting pool to ready state.