Mutithreading in java

Multitasking : 

Executing several tasks simultaneously is the concept of multitasking.

There are two types of multitasking 

1.Process based multitasking

2.Thread based multitasking

     Process based multitasking:

Executing several tasks simultaneously where each task is a separate independent process such type of multitasking is called process based multitasking

Ex: while type program in editor we can here song in same system

Thread based multitasking:

Executing several tasks simultaneously where each task is a separate independent part is called a “Thread”

How to define a Thread:

1.By extending Thread class 

2.By implementing Runnable Interface

Ex:

class Hello extends Thread{    

public void run(){

for (int i = 0;i<10;i++ ){

System.out.println("my program by extendind Thread class.....");

}}}

class ThreadDemo{

public static void main(String[] args){

Hello t=new Hello();

t.start();              

for(int i=0;i<5;i++){

System.out.println("main thread");}}}

Difference between t.start() and t.run() methods:

In case of t.start() a new Thread will be created which is responsible for the execution of run() method. But in the case of t.run() no new Thread will be created and run() method will be executed just like  normal method by the main Thread.

If multiple Threads are waiting to execute then which Thread will execute 1^st is decided by Thread Scheduler.

Activities of start():

1. Register Thread with Thread Scheduler

2. Invoke run() method

We can say that without executing Thread class start() method there is no chance of starting a new Thread in java