DEV Community: saiteja623

Multiprogramming vs Multiprocessing vs Multitasking vs Multithreading

saiteja623 — Fri, 16 Oct 2020 08:15:30 +0000

A CS Student must be aware of all the above terms. Let us have a clear explanation and clean difference between all of them.

Multiprogramming

So what is this multiprogramming ?. As the name says, Multiple programmes will get executed. So, let's understand this with example.

Consider 4 programmes say P1,P2,P3,P4 are in the main memory and need the CPU to get processed. Let us get this through a conversation

CPU : Come on P1,I will execute you .

( P1 executes for sometime and need to access I/O )

P1 : Hey CPU, I need I/O.

CPU : Okay go for it. Come on P2 , Now I will execute you.

( P1 returns to CPU after its I/O completion ).

CPU : P2 You need to wait as P1 got returned ,Again I will execute You Once if P1 gets processed or goes for I/O.

In the above, when P1 goes for I/O, CPU is idle. It will be executing the next process in the main memory i.e., P2 until P1 returns. Once P1 job is done P2 gets executed and this will go on..

The main aim of multiprogramming is to maximize the CPU utilization.

Multiprocessing

When you want to purchase a new laptop, Obviously you check the specifications of each laptop. In specifications there must be "dual-core",
"octa-core", "quad-core" .Ever wondered what these cores are?

Cores are the processors. Each core can execute a process.

dual core - 2 cores
quad core - 4 cores
octa core - 8 cores

Let's understand this through an example.

You have a building to construct and You got only one worker. It takes much long time to build right?. What If you have 4 workers instead?. As the number of workers increases, the time to complete the work decreases.

You can compare cores to the workers. If your OS is quad-core then 4 multiple core can work at a time on a single programme if and only if the programme needs 4 cores. If the programme needs only two cores then other two cores will be idle.

Multitasking

Okay. Let's say you want to listen to music and want to do coding simultaneously. This is achieved by multitasking. Chewing a bubble gum while walking is an example of multitasking.

Multitasking in single core OS

Do you think Your system really executes multiple programme concurrently?

Obviously No!

what your OS really does is, It executes each programme for a little amount of time and switches to another programme.

For example, Your OS executes Music for 5ns and it switches to editor in which you are coding and executes it for 5ns and again switches to music and executes for 5ns and this will go on.....This context switching between programmes is so fast that we humans get the illusion of multiple programmes executing at a time.Actually it is not!

Multitasking OS is also called time-sharing OS.

Multitasking in Multicore OS

Here above you have 4 tasks to run simultaneously. we have dual-core OS and each core is assigned to two tasks. In the above first core needs to run wordprocessor and E-mail. As one core can't do two programmes it uses the concept of multitasking and runs it concurrently.

### Multithreading

Threads are the main execution of a process. IN multithreading multiple threads execute a process and makes the process get executed faster.

Okay, You have opened a browser and you are surfing the web while downloading a song.

Here, One threads controls the downloading of song another thread controls the requests to the server. Other thread controls opening of new tab and these are done concurrently.

A single core OS with threads can work like dual-core.

A dual core OS with threads can work like quad-core.

That's it. If still you are unclear with the concepts, Please let me know.

Let's connect on twitter

Happy coding :)

HTML5 Tags at a glance

saiteja623 — Thu, 15 Oct 2020 11:34:00 +0000

Let us have a look at common HTML5 tags.

Document Outline

<!DOCTYPE>         <!-- Version of (X)HTML -->
<html>                <!--HTML Document-->
<head>               <!--page information -->
<body>               <!-- Page Contents -->

Page Information

<base/>       <!-- Base URL -->
<meta/>       <!-- Meta data -->
<title>          <!--Title -->
<link/>         <!-- Relevant resource -->
<style>        <!-- Style resource -->
<script>       <!-- script resources -->

Links

<a href="">                   <!-- Page link -->
<a href="mailto:">        <!-- Email link -->
<a name="name">        <!-- Anchor -->
<a href="#name">        <!-- Link to a anchor -->

Document Structure

<h1><h6>       <!-- Headings -->
<div>               <!-- Page section or a division -->
<span>            <!-- Inline section -->
<p>                  <!-- Paragraph -->
<br/>                <!--Line break -->
<hr/>                <!-- Horizontal line -->

Forms

<form>        <!-- form -->
<fieldset>    <!--collection of fields -->
<legend>     <!-- Form legend -->
<label>         <!-- Label for Input -->
<input />      <!-- Input fields-->
<select>       <!-- Drop-down box -->
<optgroup>  <!--Group of options -->
<option>     <!--Drop down options -->
<textarea>   <!--Large text Input -->
<button>       <!-- A button  -->

Tables

<table>              <!-- Table -->
<caption>          <!-- For Caption -->
<thread>           <!--Thread -->
<tbody>            <!-- Table body -->
<tfoot>              <!-- Table foot -->
<colgroup>      <!-- Column Group -->
<col/>                <!-- column -->
<tr>                   <!-- table row-->
<th>                   <!-- Header Cell -->
<td>                  <!-- Table cell -->

Lists

<ol>       <!-- Ordered List -->
<ul>       <!-- UnOrdered List -->
<li>        <!-- List Item -->
<dl>       <!-- Definition List -->
<dt>      <!-- Definition term -->
<dd>     <!-- Term description -->

Okay, I think I almost covered all common HTML Tags we often use. If I miss one in case ?, Please DO let me know!

Thanks for the read.

Lets connect on Twitter

Happy Coding :)

What exactly "static" keyword is in Java?

saiteja623 — Thu, 15 Oct 2020 11:29:42 +0000

Many of us still get confused with the keyword static. Now, we will discuss how static keyword is used? and how it helps to save lots of code from rewriting?

Look at the following code

public class staticDemo{
           public static void main(String args[]){
                     System.out.println("Hello world!");  //prints "Hello world"
            }
}

"Hello world" is the basic programme right ?.It is how someone starts learning java. Do you ever noticed that the main method has a keyword static?. What this static does?.

By using static keyword in main() method , we can call the main() method without any instance of object i.e., We can call the static methods using class name.

Let's have another example -

class A{
     static void  show(){
         System.out.println("static method in class A");
    }
}  
public class staticDemo{
           public static void main(String args[]){
                     A.show() // prints  "static method in class A"
            }
}

static variable in Java

static variables are the variables which are applicable to the all instances of the class declared it. When a variable is static its value is same for the all instances. If any one of the instance changes the static variable value it reflects to all other instances too.

consider the following code -

class A{
    static int i;
} 
public class staticDemo{
    public static void main(String args[]){
        A obj1= new A();
        A obj2 =new A();
        A obj3 =new A();
        obj3.i=10; 
       System.out.println(obj1.i); // 10
    }
}

NOTE - static variables can be accessed in non-static methods. But non-static variables can't be accessed in static methods. Why that is so?, Since non-static variables need for an instance to call the variables and we can assign different values for non-static variables by creating multiple objects. So there will be an ambiguity for the compiler to understand for which value instance value I should access.

## static block in java -

static block is used for initializing the static variables. static block is executed only when the class is loaded into the memory i.e., only once.

class A{
    static  int i;
    static{
          i=9;
          System.out.println("static block in A");
    }
}   
public class staticDemo{
    static{
     System.out.println("static block in main");
     }
    public static void main(String args[]){
              System.out.println(A.i);
               System.out.println("static in main");


    }  
}

Always static blocks are executed first. static block gets executed and then main() method gets executed. In main() method we have A.i here A class gets loaded into the memory and when memory is loaded static block gets executed and then the value of i gets printed, at last "static in main" gets printed.

// output of above code
static block in main
static block in A
9
static in main

Summary

variables and methods with the static keyword do not need an instance to access it. They can be accessed using class name.
static blocks are executed before constructors and methods.
If there are multiple static blocks, they are executed as per the sequence in the code.
non-static variables can't be accessed in static methods.

Thanks for the read!. I hope you have learnt something about static. If you feel something wrong please let me know :)

Let's get connect on Twitter.

Happy coding :)

Multithreading in java

saiteja623 — Sat, 10 Oct 2020 09:20:49 +0000

Multithreading is the one which we often come across in java. So, What actually Multithreading is?, What it does?, why it is needed?.

Let us consider the following code

public class Multithreading{
          public static void main(String args[]){
             System.out.println("hello");
}
}

In the above code we can see Output is "hello"

So how this code is running? , Every Java programme has main Method and the main method gets executed. Here main method is a thread.

How to create Threads in Java?

Now Let us make multiple threads in java

class A extends Thread{
    public void run(){
        for( int i=0;i<5;i++){
        System.out.println("hi");
    }
    }
}
class B extends Thread {
    public void run(){
        for(int i=0;i<5;i++){
        System.out.println("hello");
        }
    }
}
public class multithreading{
    public static void main(String args[]){
            A obj=new A();
            B obj1=new B();
            obj.start();
            obj1.start();
    }
}

java
In the above code ,We have two classes :

Class A
Class B

In order to provide a single thread for each class. We need to extend the Thread class and the code which thread should work upon will be written in the run() method and how do we call this run method? .We create a Object for each class and we call start() method. start()method is located in the Thread class. This start() method starts the execution of the thread.

The output is different in different cases as we can't print different outputs at the same time .One is choosen between them based on some criteria and priorities.

//output1
hi
hello
hi
hello
hi
hello
hi
hello
hi
hello

//output2
hi
hello
hello
hi
hello
hi
hi
hello
hi
hello

Now we have 3 Threads

class A thread
class B thread
main() thread

we should not override the start() method in Thread class by defining it in class A and B. This calls the start() method in the child class rather than parent class and which no longer acts like a thread.

What's the problem here?

So we have a problem here :(. What if I want to extend both Thread and other class. Let's say I want other class C which extends class A and Thread.

class C extends A,Thread{
           //code
}

Wait!. This is multiple Inheritence. Unfortunately we don't have multiple Inheritence in Java. Then how to overcome this?.

Multiple Inheritence can be overcome by Interfaces. We do have a interface called Runnable Interface in Which a class can implement Runnable Interface.

class C extends A implements Runnable{
      //code
}

We are not getting into the Runnable Interface. We will discuss it in the next Article in depth.

Applications of Multithreading

There are lots of applications of Multithreading. Let's say you are playing game like PUBG. You can move and your friend can move and the sound effects when someone shoot these actions are performed simultaneously by different threads.

Summary

Threads are like workers who are need to construct a building
Multiple Threads can work at a same time.
Class should extends the Thread class and should have a run() method defined inorder to work as a seperate Thread.
Create a object(obj) for the class. Call the run() method by obj.start()

Thanks for the read!. If something feels wrong, please let me know.

Happy coding :)