Multithreading in Java

Introduction

So far you would have been learned about a single thread. Lets us know about the concept of multithreading and learn the implementation of it. But before that, lets be aware from the multitasking.

Multitasking :

Multitasking allow to execute more than one tasks at the same time, a task being a program. In multitasking only one CPU is involved but it can switches from one program to another program so quickly that's why it gives the appearance of executing all of the programs at the same time. Multitasking allow processes (i.e. programs) to run concurrently on the program. For Example running the spreadsheet program and you are working with word processor also.      
Multitasking is running heavyweight processes by a single OS.

Multithreading:

Multithreading is a technique that allows a program or a process to execute many tasks concurrently (at the same time and parallel). It allows a process to run its tasks in parallel mode on a single processor system 

In the multithreading concept, several multiple lightweight processes are run in a single process/ task or program by a single processor. For Example, When you use a word processor you perform a many different tasks such as printing, spell checking and so on. Multithreaded software treats each process as a separate program.

In Java, the Java Virtual Machine (JVM) allows an application to have multiple threads of execution running concurrently. It allows a program to be more responsible to the user. When a program contains multiple threads then the CPU can switch between the two threads to execute them at the same time. 
For example, look at the diagram shown as:

In this diagram, two threads are being executed having more than one task. The task of each thread is switched to the task of another thread.

Advantages of multithreading over multitasking:  

• Reduces the computation time.
• Improves performance of an application.
• Threads share the same address space so it saves the memory.
• Context switching between threads is usually less expensive than between processes.     
• Cost of communication between threads is relatively low.

Different states in multi- threads are-

• Sleeping – On this state, the thread is still alive but it is not runnable, it might be return to runnable state later, if a particular event occurs. On this state a thread sleeps for a specified amount of time. You can use the method sleep( ) to stop the running state of a thread.
        
       static void sleep(long millisecond) throws InterruptedException
  
• Waiting for Notification – A thread waits for notification from another thread. The thread sends back to runnable state after sending notification from another thread.
         
       final void wait(long timeout) throws InterruptedException
       final void wait(long timeout, int nanos) throws InterruptedException
       final void wait() throws InterruptedException
       
• Blocked on I/O – The thread waits for completion of blocking operation. A thread can enter on this state because of waiting I/O resource. In that case the thread sends back to runnable state after availability of resources.
       
• Blocked for joint completion – The thread can come on this state because of waiting the completion of another thread.
      
• Blocked for lock acquisition – The thread can come on this state because of waiting to acquire the lock of an object.