Java-LinkedinLearning

This repository consist of Java Learning and basic notes taken from the Linkedin Learning and udemy //written By Swapnil Gupta (twitter)[https://twitter.com/insanity_xi]

• first course is on Java Basics: (Linkedin Learning)[https://www.linkedin.com/learning/learning-java-4]
• Second is on Java OOPs : (Linkedin Learning)[https://www.linkedin.com/learning/java-object-oriented-programming-2/what-is-object-orientation]

1-Basics

• JDK= JRE, compiler and Tools
• IDE= Editor, debugger and tools

Java codes needs compilation first then execution

>> javac HelloWorld.java
>> java HelloWorld

Whereas the code can be written in file as such:

//HelloWorld.java
public class HelloWorld{
    public static void main(String[] args){
        System.out.println("Hello World!");
    }
}

Main Function-

each file has main function

main function: Runtime system, Code must be connected to this to call and in order to be executed by the program

difference between main function and regular function is main function is called automatically whereas other function is need to be called.

-will be sharing more details on function in "Functional Programming:Java" Repo

Function in Java:

function is series of finite steps to complete the task.

• Designed once, used many times
• orgnize code, easy modification

A function needs to be -
Defined - outside main function
-public static void functionName(){
setps
}
Used- inside main function
-fuctionName();
-Syso(functionName()); //syso is shortHand for system output

Returned- each function either return a void value or a datatype.

to get the dynamic values we pass the parameters and argument through input, arguments are the actual values.

2- Java OOPs:

everything can be converted to code

OOPS: object oriented programming model based around objects and data

-it makes easier and reusable code -attributes and Behaviour makes and object

Eg. TREE

-attributes: height, trunk diameter
-Behaviour: ability to grow

Object Oriented Progamming comes with four pillars

-- Abstaction
-- Inheritence
-- Encapsulation
-- polymorphism

Classes-

we can model attributes and behaviour of objects as blueprint that defines object. It has combination of variable and function.

a class can create multiple objects.
class -> object1, object2

eg: Triangle :

-attributes: base, height, s1, s2, s3 -behaviour/method: area(), type()

we have to add the static keyword to, if function does not use the attribute of the class but relates to overall idea.

Constructor class -

a constructor is method or behavior inside every class that creates and initialised the instances.

instance - an object created from class blueprint. eg: Triangle1 from triangle class

• A constructor always returns an instance of the class it is in. having same name of class, i.e. constructor of triangle class return triangle

pubilc triangle{
    public triangle(){
       
    }
}

this keyword- to access the attribute for the triangle instance we are trying to create we use this keyword.

eg:
this.base=base;
this.height= height;
this.s1=sidelen1;
this.s2=sideLen2;
this.s3=sideLen3;

we call constructor with new keyword in main as we are creating new instance.

a constructor also initalizes all the attributes with dynamic values,i.e. the values of constructor is called with, determine the values of attributes.

creating a class

public class Main{
    public static void main(String[] args){
        //some code
        //
    }
}

instance method vs class method

• instance method are non-static method, and it needed an instance to use. can be dynamically changed.
• class method are called as static method because no need of instance.

similarly, there are static and Non-Static variables.

Objects: