Java Multithreading

Question 1

What is Multithreading ?

Answer 1

Multithreading is when a program contains two or more parts which can run concurrently even with different tasks.
=> Java is a Multithereaded language.

Question 2

How to achieve multithreading

Answer 2

you need java.lang.Thread class

Question 3

Thread Life Cycle

Answer 3

*New: it is known also as born thread , it’s the beginning state of a thread.
*Runnable:once a thread is born thread , we can execute it (in this state thread considered to be executed).
*Waiting: a thread transitions to waiting state, waiting a signal from another executed/runnable thread
*Timed Waiting: after an interval of time expires a thread can execute or also if the thread which wait for is executed.
*Terminated(Dead):is the state where a thread complete its task.

Question 4

Thread Priorities

Answer 4

Java thread priorities are in the range of MIN_PRIORITY ( a constant of 1 ) and MAX_PRIORITY( a constant of 10 ) by default each thread have NORM_PRIORITY(a constant of 5 )

Even though a max_priorities has more proriety to be executed first by program , it doesn t guarantee execution order of threads and thread priority is a platform dependant.

Question 5

Create a thread by implementing Runnable interface

Answer 5

*Implement run() method:Here we write our business logic code.
*Instantiate a thread Object:you can instantiate using this Thread constructor :
Thread(Runnable threadObj, String threadName) where threadObj is name of class that implements Runnable or extends Thread(second arg (threadName) is optionnal).
*Call thread using start() method: run thread, we can also override it and do instantiation inside it

Question 6

Create a thread by extending a Thread Class

Answer 6

Same steps of implementing Runnable interface, the difference is we extend Thread class instead of implementing Runnable interface and it give us more flexibility with Thread class methods.

Question 7

Some Thread Class methods

Answer 7

start(),run(),setName(),setPriority(),setDaemon(), join(),interrupt(),isAlive(),sleep()
*setDaemon(): A thread becomes a daemon thread
*join():it is invoked on a second thread causing the current thread to block until the second end or time expire
*interrupt():Causing a thread to continue if it was blocked , if not blocked , it is interrupted until other threads execute.

Question 8

Daemon Thread

Answer 8

A daemon thread is created to support user threads.Once all threads are closed , daemon thread terminates. example Garbage collector.

Question 9

JVM Shutdown Hook

Answer 9

*Controlled process:happens if System.exit() method is called or with Ctrl+C or if the last non-daemon thread terminates
*Abrupt manner: happens after a kill signal , with Runtime.getRuntime().halt() call or an OS menace.