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Java Notes

Important Links



Java -
Required softwares and tools -
----------------------------------
JDK - 11+
MySQL - 8
IDEs - Eclipse(Spring Tools IDE), Visual Studio Code
----------------------------------------------------
Java - 
 * Object Oriented
 * Dynamic
 * Platform Independent


JDK - Java Developmemt Kit
JRE - Java Runtime Environment
JVM - Java Virtual Machine

----------------------------------------
Basic building blocks in Java
-----------------------------------------
keywords,
identifiers
literals,
variables,
methods,
classes,
objects
---------------------------------------
Using variables in java:
-----------------------------
data-type variable-name;

Data-types
-------------------
Primary :
----------
byte - 1 byte integer value
short - 2 bytes integer value
int - 4 bytes
long - 8 bytes
float - 4 bytes (20.67F, -0.00054f)
double - 8 bytes (20.54630817)
char - 1 Byte / 2 Bytes ('a','-','5')
boolean - 1 Bit (true/false)

Secondary :
--------------
arrays
enum 

User defined types:
-------------------
class
interface


Java Naming Standard :
------------------------
Class naming rule :
----------------------
	Should always start with an Uppercase and follow the Camel casing
		- Scanner, BufferedReader

Variables/Method naming rule :
-------------------------------
	Should always start with a lowercase and follow the Camel casing
		- main(),username, nextInt()

Package naming rules :
-----------------------
	Should be in lowercase only

Final fields/constants :
--------------------------
	Should be in uppercase only

		final double PI=3.14;

Assignments : Day1

-- Complete the first four challenges -- https://www.hackerrank.com/domains/java

Important Links

Topics for self learning - String Methods, String vs StringBuilder



Inheritance
--------------

Item - name, price, id
Phone - ram, storage
Laptop - ram, storage, os

				Vehicle		- super class [name,regno]
			  /		\	\
			 /		 \	 \
			/		  \	  \
		Bus			 Car Bike	 - sub class
	[capacity]	 /\
					/  \
			Electric Petrol


bus - horn()
car - musicSystem, play()
bike - boolean abs, accletate()


Car car = new Vehicle();


class Item{		
	....
	....
}

class Laptop extends Item{
	
}

 ** private and static properties wont be inherited


Abstraction:
--------------
Item -
	id, name, price
	abstract void showItemDetails();
	setPrice()

ElectronicItem extends Item -
	showItemDetails()
	...

Clothing extends Item -
	showItemDetails()
	...


Abstract Class - 
	contains abstract methods
	cannot create object of any abstract class
	extending the abstract class and overriding the abstrat methods are necessary





Multiple Inheritance :
------------------------

		A		B
		\		/
		 \	  /
			C

A{
fun(){
	...
 }
}

B{
fun(){
	...
 }
}

class C extends A,B{

}

Interfaces -
------------------
an interface looks like a class but it can have only abstract methods and final fields



When to choose abstract class over interface and vice versa?
-------------------------------------------------------------

Item - price, name

WrittenItem extends Item - author
Book extends WrittenItem - isbn, pages
Journal extends WrittenItem - publishedDate

MediaItem extends Item
....

Interfaces are used for runtime ploymorphism and to acheive loose coupling


Method Overloading
----------------------
 method with same name but different signatures within the same class
	- no of arguments, type of arguments

class Calculator{
	int add(int a, int b){
		return a+b;
	}
	
	int add(int a, int b, int c){
		return a+b+c;
	}

	float add(float a, float b){
		return a+b;
	}

}

main(){
	Calculator calc = new Calculator();
	calc.add(4,5);
	calc.add(4.5f,3.4F);
	calc.add(3,8,6);
}


 notes.txt

 lotus.jpg

 profile.pdf


Overloading vs Overriding
---------------------------


Object class methods :
-------------------------
String toString()
boolean equals()
int hashCode()


Collection Framework
-------------------------
Limitations of Arrays -

* Fixed size
* Items can not be removed
* Accessing through index only
* no well define algorithms are present

Collection Framework
--------------------
API - Application Programming Interface
Consists of different interfaces and classes


Layered Architecture
----------------------

Presentation Layer - For interactiong with clients

Business Layer - Business Logic and service classes

Persistence Layer - DAO (Data Access Object) contains storage logic

Database - Conatins the database

Database Notes



DBMS - Database Management System

Relational
------------
MySQL, SQLServer, Oracle, Postgres


Non-Relational (NoSQL)
-----------------------
MongoDB, Amazon DynamoDB

SQL - Structured Query Language
-------------------------------

Employee, Student, Laptop - Entities

Tables - Rows/Records/Tuple	| Columns/Fields/Attributes

-----------------
SQL
------
	DDL - Data Defn. Language
		- create, alter, drop, truncate

	DML - Data Manipulation Language
		-	insert, update, delete

	DQL - Data Query Language
		- select

	DCL - Data Control Language
		- grant, revoke

	TCL - Transaction Control Language
		- COMMIT, ROLLBACK, SAVEPOINT

Tips

empno - numeric(4)
ename - varchar(30)
job - varchar(30)
hiredate - date
mgr - numeric(4)
sal - numeric(6,2)
comm - numeric (6,2)
deptno - numeric(2)

HTML topics to go through -

  • HTML Lists
  • HTML Tables
  • HTML Form Elements
  • Links
  • Divs

Angular Recordings

https://drive.google.com/drive/folders/1HebnyjDMsC-7-h2J3F5s-BxwDGwJ5fYZ?usp=sharing