DEV Community: Pavithra Saravanan

System.out.println in Java

Pavithra Saravanan — Mon, 06 Jan 2025 15:22:46 +0000

Java System.out.println() is used to print an argument that is passed to it. [TBD]

Parts of System.out.println()

The statement can be broken into 3 parts which can be understood separately:
System: It is a final class defined in the java.lang package.
out: This is an instance of PrintStream type, which is a public and static member field of the System class.
println(): As all instances of the PrintStream class have a public method println(), we can invoke the same on out as well. This is an upgraded version of print(). It prints any argument passed to it and adds a new line to the output. We can assume that System.out represents the Standard Output Stream.

System and PrintStream package

As we know, Method Overloading in Java allows different methods to have the same name, but different signatures or parameters where each signature can differ by the number of input parameters or type of input parameters or both. From the use of println() we observed that it is a single method of PrintStream class that allows the users to print various types of elements by accepting different type and number of parameters.

For example:

System.out.println(),
System.out.println(int),
System.out.println(double),
System.out.println(string),
System.out.println(character),
etc.

Reference link:https://www.geeksforgeeks.org/system-out-println-in-java/

Java Constructor

Pavithra Saravanan — Mon, 06 Jan 2025 15:07:54 +0000

What is constructor?
A constructor in Java is a special method that is used to initialize objects. The constructor is called when an object of a class is created. It can be used to set initial values for object attributes.

A constructor must have the same name as the class it belongs to.
Constructors are automatically called when an object is created using the new keyword.
Constructors are used to initialize the object's data members and set up the initial state of the object.

Types of Constructors:

Default Constructor:
If you don't explicitly define any constructors in your class, the Java compiler will automatically provide a default constructor. This constructor takes no arguments and initializes the object's fields with default values.
Parameterized Constructor:
A parameterized constructor allows you to pass values as arguments when creating an object, enabling you to initialize the object's fields with specific values.
Copy Constructor:[TBD]
A copy constructor is used to create a new object that is a copy of an existing object of the same class.

What is this keyword?

There can be a lot of usage of Java this keyword. In Java, this is a reference variable that refers to the current object.

Usage of Java this keyword

Here is given the 6 usage of java this keyword.

this can be used to refer current class instance variable.
this can be used to invoke current class method (implicitly)
this() can be used to invoke current class constructor.
this can be passed as an argument in the method call.[TBD]
this can be passed as argument in the constructor call.[TBD]
this can be used to return the current class instance from the method.[TBD]

Reference link:
https://www.javatpoint.com/this-keyword

Task 2(28/12)

Pavithra Saravanan — Sun, 29 Dec 2024 10:59:13 +0000

Task 2:

Create a class called 'Shop'
Create below static variables: static int doorNo = 5; static int discount = 10; 2.1. Create below non-static variables int price, weight;
Create main method.
Inside main method, create instance as below Shop product1 = new Shop(); Shop product2 = new Shop();
Using product1, assign price and weight.
Using product2, assign price and weight.
Call a non-static method as below. product1.bill(); product2.bill();
Save, Compile and fix the error.
Inside bill() method, print price and weight.
Inside main method and inside bill() method, print doorNo and discount

public class Shop
{
static int doorNo = 5;
static int discount = 10;
int price,weight;
public static void main(String[] args)
{
Shop product1 = new Shop();
Shop product2 = new Shop();
product1.price = 550;
product1.weight = 1000;
product2.price = 150;
product2.weight = 50;
System.out.println("Doorno:"+doorNo+ " Discount:"+discount);
product1.bill();
product2.bill();
}
public void bill()
{

System.out.println("Price:"+price+ " Weight:"+weight);
}
}

Output:

Task 1(28/12)

Pavithra Saravanan — Sun, 29 Dec 2024 10:43:33 +0000

Task 1:

Create a class called 'Jewellery'
Create below static variables: static int goldPrice = 7100; static int silverPrice = 150; 2.1. Create below non-static variables int making_charges, wastage;
Create main method.
Inside main method, create instance as below Jewellery jewel1 = new Jewellery(); Jewellery jewel2 = new Jewellery();
Using jewel1, assign making_charges and wastage.
Using jewel2, assign making_charges and wastage.
Call a non-static method as below. jewel1.bill(); jewel2.bill();
Save, Compile and fix the error.
Inside bill() method, print making_charges and wastage

Code:

public class Jewellery
{
static int goldPrice=7100;
static int silverPrice=150;
int making_charges,wastage;
public static void main(String[] args)
{
Jewellery jewel1 = new Jewellery();
Jewellery jewel2 = new Jewellery();
jewel1.making_charges = 15000;
jewel1.wastage = 140;
jewel2.making_charges = 50000;
jewel2.wastage = 5000;

jewel1.bill();
jewel2.bill();
}
public void bill()
{
System.out.println("Making charges:"+making_charges+ " Wastages:"+wastage);
}
}

Output:

Java basic program with expansion

Pavithra Saravanan — Thu, 26 Dec 2024 10:13:16 +0000

Created a class as public class Library
Created a object as Library books = new Library();
Object is memory representation of class.
Most important object name should not be in capital.

How to create an object in Java? {TBD}

Java provides five ways to create an object.

Using new Keyword
Using clone() method
Using newInstance() method of the Class class
Using newInstance() method of the Constructor class
Using Deserialization

Code:

public class Library
{

public static void main(String[] args)
{
Library books = new Library(); //Object Creation
//new allocates memory - Instance - Instantiation
books.fiction(); //Method Calling Statement
Library librarian = new Library();
librarian.lending_books();

}
public void fiction() //Method Signature
{
//Method Definition / Body
System.out.println("Book Name:Fiction books");
}


public void lending_books() //Method Signature
{
//Method Definition / Body
System.out.println("Librarian:Successfully lended the books");
}


}

Output:

OOP (Object-Oriented Programming)

Pavithra Saravanan — Thu, 26 Dec 2024 06:31:51 +0000

Object means a real-world entity such as a pen, chair, table, computer, watch, etc. Object-Oriented Programming is a methodology or paradigm to design a program using classes and objects. It simplifies software development and maintenance by providing some concepts:

Object
Class
Inheritance
Polymorphism
Abstraction
Encapsulation

Object
Java Object

Any entity that has state and behavior is known as an object. For example, a chair, pen, table, keyboard, bike, etc. It can be physical or logical.

An Object can be defined as an instance of a class. It contains an address and takes up some space in memory. Objects can communicate without knowing the details of each other's data or code.

Class
Collection of objects is called class. It is a logical entity.

A class can also be defined as a blueprint from which you can create an individual object. Class does not consume any space.

Step By Step Code Execution in Java (using linux)

Pavithra Saravanan — Thu, 26 Dec 2024 06:27:01 +0000

The developer or programmer writes the code in a human-readable format. Java compiler compiles it into byte code.
Byte code is not the machine executable code and hence, requires an interpreter to interpret it. The interpreter is the Java Virtual Machine (JVM) that executes the Byte code.

Compilation and execution
Two step process that involves converting the source code into executable code.

The first step compile the source code into byte code using Java compiler (javac)
Execution step is to run the byte code using JVM.

To fix your Linux after installation

Step 1: Go to update manager

Step 2: Install updates Check its upto date

Step 3: Select view and click linux Kernels.

Step4: Warning pop up will appear click continue then check whether it is in latest version.

Step 5: Now your Linux Os is ready to use.

In linux open text editor
Select edit and click preferences
In Display check the display, line numbers.
Choose plugins and check the needed checkbox.

Now type the code in text editor:

public class First
{
public static void main(String[] args)
{
System.out.println("Welcome To Java");

}

*After typing the code press ctrl+s

*Pop up will appear click documents create a folder and name it after that keep a file name most important thing keep he class name as file name.

Open the terminal and type is to view the list of documents.

Now go to files and choose doc folder (B14) in that
right click and press open in terminal

The terminal will be opened type the command javac First.java
It will ask to install jdk in that choose the option yes.

After that list of jdk will appear in that select and copy sudo apt install default - jdk.

Please wait for few minutes until it gets completed then type the comand java filename.

Output will appear:
Welcome to java
Java first change the source code into byte code then convert into binary code.

 compiler

will check error
and trans into byte code
Java --------------> Byte code -------> Binary code

     Checking error
       compiler

.java file ---------> .class file --------> common for all
platforms.

Java

Pavithra Saravanan — Thu, 26 Dec 2024 06:15:34 +0000

Java is a popular programming language.

Java is used to develop mobile apps, web apps, desktop apps, games and much more.

What is Java?
Java is a popular programming language, created in 1995.
It is owned by Oracle, and more than 3 billion devices run Java.
It is used for:
Mobile applications (specially Android apps)
Desktop applications
Web applications
Web servers and application servers
Games
Database connection
And much, much more!

Why Use Java?
Java works on different platforms (Windows, Mac, Linux, Raspberry Pi, etc.)
It is one of the most popular programming languages in the world
It has a large demand in the current job market
It is easy to learn and simple to use
It is open-source and free
It is secure, fast and powerful
It has huge community support (tens of millions of developers)
Java is an object oriented language which gives a clear structure to programs and allows code to be reused, lowering development costs
As Java is close to C++ and C#, it makes it easy for programmers to switch to Java.

Platform Independence:
Java is a class-based, object-oriented programming language that is designed to have as few implementation dependencies as possible. It is intended to let application developers write once and run anywhere.

Linux

Pavithra Saravanan — Thu, 26 Dec 2024 06:10:18 +0000

Linux is an open-source operating system (OS) that is used in many different computing devices, including PCs, servers, and mobile devices. It's known for its reliability, security, and versatility, and is used in some of the world's most powerful supercomputers.
Linux is free to install and use on as many computers as you like.

Reference link:https://www.geeksforgeeks.org/introduction-to-linux-operating-system/

How to install Linux:

First download Linux mint Cinamon download link:https://linuxmint.com/edition.php?id=316

After that download Rufus 64-bit suitable version for your windows

Connect USB-pendrive run rufus then choose your USB and select the Linux mint disc image.

Partition scheme must be in GPT and click the start to convert into bootable.

After that it takes few minutes to complete when the status Ready then close the window.

Restart your pc and press boot menu (F9) or according to your pc.

Reference link:https://revathi22.wordpress.com/2024/07/27/dual-boot-windows-11-and-linux-mint-step-by-step-guide/

Compiler/Interpreter

Pavithra Saravanan — Thu, 26 Dec 2024 06:02:29 +0000

              Translate to

Human language <-----------------> Machine language
Interpreter/
Compiler
Machine language
Assembly language ----Formula trans------Fortran
High level language

Fortran programming language:
Fortran is a programming language used for scientific and numerical computing.

Fortran was developed by IBM in the 1950s and was the first computer language standard. The name is short for "Formula Translation".

COBOL programming language:
COBOL (Common Business-Oriented Language) is a high-level programming language used for business applications.

After that
Dennis Ritchie invented C
Guido invented python
Sun microsystems invented Java

JDK
The Java Development Kit (JDK) is a cross-platformed software development environment that offers a collection of tools and libraries necessary for developing Java-based software applications and applets. It is a core package used in Java, along with the JVM (Java Virtual Machine) and the JRE (Java Runtime Environment).

JRE:
JRE should be installed to convert .class file into binary code
Java Runtime Environment (JRE) is an open-access software distribution that has a Java class library, specific tools, and a separate JVM. In Java, JRE is one of the interrelated components in the Java Development Kit (JDK). It is the most common environment available on devices for running Java programs. Java source code is compiled and converted to Java byte code. If you want to run this byte code on any platform,you need JRE.

JRE---->Jvm---->JIT compiler

Library:
Collection of java program it would be in .class file

JRE will collect .class file trans that file into binary code.

.java -------> .class ---------> Binary
jdk byte JIT compiler
code
Java is both compiled and interpreted language.
JIT compiler-Interpreter
Interprretation: Line by line translation.

Introduction

Pavithra Saravanan — Wed, 25 Dec 2024 15:22:40 +0000

Intro of Computer:
Computers are electronic devices designed to process data and perform tasks according to instructions.

Main components of a computer:

CPU Brain of PC
Memory RAM Storage of data
Storage HDD/SSD
Motherboards Main circuit board
Power Supply Unit convert electricity from outlet
Input Device Keyboards, mouse etc
Output Device Monitors, Speakers ck
Graphic Processing Unit Graphic design
Cooling System Fans

Father of computer:
Charles Babbage Invented the concept of Analytical Engine in 1837

The Analytical engine contained an Arithmetic Logic Unit (ALU) basic flow control and integrated memory which led to the development of first general purpose Computer concept.

Reference link:(https://drive.google.com/file/d/18B_iG_TVKwD1WXtwtyXZXNe8KRbcKm3r/view
)