Core Java

Core Java- 19/5(Intro,Features,JDK/JRE )

Features

Simple
Platform Independent
High Performance
Java is 100% object oriented everything is in class in c++ you can write main outside classs.
java is compiled and intrepeted language.
JIT(Just in Time) Compilier:-
- work just before execuation.
- It conver some part of code directly into machine understanding.
because of this language become faster it avoid read and convert time.
Security over the internet
Robust(strong/tough)
- Automatic Memory Management
- Expection Handelling
Multithearding(multitasking)
Distributed(Remote Server involved)
Dynamic

JDK/JRE

First Program

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

When the class is decleared as public then the name of program should be class name..
static method can called without object creation thats why used in main.
out is the object called for print, out object is accessible using System class.
println() is a method.
At least one class should be public because of main().
Class name always should be start with capital.
System=Class, out=object, println()=function.
Setting path of java/javac(for setting epath of java and javac you need following steps.).

for run program javac programName.
javac -version is used to check the version of java.
*Bytes code(.class) always based on class name,if program name and class name is not equal then .class file name will be class name not a program name. *
javac programName
java .classFileName

20/5 (OOPs,Major and Minor piller)

Introduction of Object Oriented Programming

Procedural Programming

* It made with the functions.
* Co-ordinate with `main()`.
* Not working with entity.
* Real life modelling is not possible.
* Data Security (primery focous on procedurse not security)
* After some code modification of code is difficult.

To overcome from this disadvantage they come up with new concept i.e OOP

Object Oriented Programming

Object

It is instance of the class
It representing real life entity- customer,student, account
Object has some state and behavior.
Every object has some identity and role to be play in system
Some objects are actually physically present those are called as tangible entity/object.(eg. student, laptop,hard-disk)
Some objects are not actually physically present those are called as non-tangible entity/object (eg. data, account,software)
Object is something which present the real life tangiable non tangable entity which have some identity and role to be played.
State and behavior of objects
- Set of values given to the common attributes which are used for describing the object.
- State is description of the object.
- Eg. there is a car which has some compay name,color,number..etc
- So if the object is MyCar then the state of the object are Maruti,Black,mh14p8254..etc
- State is the description of object.
- There is some functionality/behavior/role of object like car speed in program it is like function.
- State= Set of values
- Identity is one of the state value which has some unique identity.

Four Major Piller of OOP

Major Piller

Abstration
Encapsulation
Inheritance
Polymorphim

Minor Piller

Strong typing
Concurrency
Persistance

Minor Piller

1) Strong Typing

Perticular type of input of way of typing or wiritng code.

2) Concurrency

Simultaneous Execution eg. Notepad spelling check

3) Persistance

Perment Storage/Database

Major Piller

1) Abstraction

Selective ignorance
It helps in reducing the complixity of code.
Process of seperation which take what is needed.
It focous on what is needed/required and discart everything else.

2) Encapsulation

State(data) and Behavior(function) are inseparable thats why we use Encapsulation
State and behavior will always together bundled into one unit is clalled Encapsulation.
Advantage- 1.Data hiding/helps to restrict access of data
2.Data Binding
3.Complex functionlity can be hidden so that simple UI is used for use of object.
4.Hide Complixity and give simple functions to the user
Class is the best example of encapsulation.

3) Inheritance

Its about the "is a" relationship.
If t entity having "is a" relationship then there is Inherantance.
Adventage 1.Reusability/reusing of code.
2.It creates the basics of polymorphism
Spealize entity from existing generalize entity by adding some extra state and behavior.

4) Polymorphism

Polymorphism:- Same massage given to common entity of different object.(different function defication)
Encaspulatio Unit

class Date
{
	// state and beahvior 
	// data members(private) + member methods(public)
	private int dd;
	private int mm;
	private int yy; //state members 
	
	public void showDate()
	{
		System.out.println(dd+"/"+mm+"/"+yy);
	}
{

public class DateDemo
{
	public static void main(String args[])
	{
		Date d1;		//Referance variable decleration
		d1 = new Date();	//object creation
		d1.shoowdate();
	}
}

Download and see code here

21/5 (Data Types, Memory Management, Constructor, this)

Data Types

Value type (premative) int,char,short,double,float eg. char ch;
Referance type (referance/non-premative(in c/c++)) class,array,interface eg. Date d1;

Memory Management in java

main method variable is in stack.
Object are stored in heap.
new is going to create to object in heap
heap data members(data in heap/object) are always initilize value 0.
Default value of object variable is 0.
Garbage collector is actually removing the unreferancing objects from the heap.
In java in switch case you can use int abd string also.
One advanced for loop(each for) is added in java.
Class(acts as encapsulation unit) never occupy any memory.

Constructor

Is the function have same name as class.
If you dont write constructor there is default constractor(zero argument).
It has no any return type.
There is two type of constructor 1. parameterise 2.non-parameterise.
If you dont write any constructor then the default will be there if the you pass with argumrent you have to write the cinstructor.
If you write paramatrised constractor then the default is not avalible.
We can write N number of constructor but parameter should be different. No constructor :- Default constructor call Constructor with parameter :- have to define parametrised constructor Both (para/non para) :- Both are avalible but parameter constructor have to define (eg. con(), con(int a, int b))
Constructor follow all the rules of polymorphism.
Constructor assign the local variable value to instance variable.
which constructor will use is depends on creation of object.
If you create a object of parameterised constructor then only parameterised constructor will call

this

this is the referance is refering to the current object(for which constructor is called)

Refer last point of constructor.

  instance variable = local variable
  this.dd = dd;
  this.mm = mm;
  this.yyyy = yyyy;

We are assigning the local variable to the instance variable.
Download and see code here

22/5 (Garbage Collector, Array)

revise

Garbage Collector

Static
Static can access only static data
Non static access both static and non static

static block,static method,static variable

Static , Array covered portion

Download and see code here

24/05 (Association Relation, Wrapper Classes)

Referance equality

Association Relationship/has a relationship

General rule of Encaplusation is declear Data Member as private and method public.

class Person
{
   private String name; //instance/non static-has
   private Date bdate;  //referance variable-has
   private int age;     // value type variable
   
   //person has name
   //person has birthday
   public Person(String name, int dd,int yy,int mm )
   {
   	this.name=name;
   	this.bdate=new Date(dd,yy,mm);
   }
}	
class Date
{
   	int dd,yy,mm;
   	public Date(int dd,int yy, int mm)
   	{
   		this.dd=dd;
   		this.mm=mm;
   		this.yy=yy
   	}
}

class PersonMain()
{
   public static void main(String args [])
   {
   	Person p1 = new Person("Shree",07,97,08);
   }

}

One object inside/contain other object is called has relationship.
Object within object.
Instance of one class contain instance of another class is called has a relationship.
Reusing the class
If you do not assign any value to referance variable it will treat as null.
name and bdate will be null if you dont assign anything to it.
In Value type variable if you dont assign anything then it'll be zero.
int age will be zero if you dont assign anything to it.
you cannot call methoth on null referance you will get error called null pointer expection.
Person is container and and bdate is component.
Adventage:- reusability.

Object Array

public class ObjectArray
{
	Date [] datearr;
	datearr = new Date[3];
	datearr[0]=new Date();
	datearr[1]=new Date(11,12,99);
	datearr[2]=new Date(12);
	
	// Short cut
	//Date[] datearr = {new Date(),new Date(11,12,99),new Date(22)};

for(int i=0;i<datearr.lenght;i++)
{
	datearr[i].showdate();
}
}

Wrapper Class

Is the classes which is replaced to treditional variables for using 100% oops concepts.
Example:-

	int i=10;
	Integer obj = new Integer(23);
	Integer obj = i; //autoboxing feature-no need to write new  
	// obj is object
	//i is value
	int num = obj; //auto unboxing

It assign object to integer(auto unboxing) and integer to object(auto boxing)
Because of wrapper class java is pure object oriented.
There are 8 premative data type so there is 8 wrapper classes.
Specifically Wrapper classes used in collections.
Download and see code here

25/05 (Packages,IDE)

Packages

Packages is a namespace/collection of classes interfaces and sub-classes.
Conceptually its a File Manager/File system in our mobile and PC.
Easy to manage the things.
File with same name but in different folder (avoid name conflicts).
Example of build in package java.lang is base and java.io,java.util,java.sql are sub packages.
You can create your own package.
Package name always should start with small letter.
To start package you have to just put package package_name;.
Always start your program with package include.
Sub packages are imported as package package_name.sub_package;
When package is complied packages are reflected in folder hierarchy.
Helps in reusability.
Build in package java.lang API.

Package name should be short and small letter.
Command for package compile javac -d dirpath javafilename

Eclipse IDE

It gives Development support
Eclipse is developed in JAVA
Plugin is avalible for extra features.
Workspace is a current working directory that has to be selected when eclipse is started
Perspective is combinition of views and editors that are required for a perticular type of application.
Use ctr+space for auto complete.
In project there is option Build Automically so thats why its compiling when you typing code.
Right click on code then source then generate const from superclass for creating constructor/with field(parameterized) autumatically.

Download and see code here

26/05(Inheritance,super(),Overriding, Dynamic Binding, Debug, Scanner)

Inheritance

It has is a relationship.
Creating specialized entity from existing generalized entity by adding extra state and behavior.
Person- name and bdate is state -display()
Emp- empid,salary bev - calSalary()
extends is keyword for inheritance.

	class Emp extends Person
	{
		//person is parent/super class
		//emp is child/sub class
	}

It found is a relationship with each others.
It used for reusability.
Child class recive data members and methods.
Private members are restricted within the class so not avalible for child.
Super() is for accessing super class constructor.

We can access any constructor with the help of super()
super always should call first in subclass.
super() is a representation on the default constructor of the super class.
So if you dont write, it will defaultly call default constructor of super class.
Two methods of same name can be same in super and sub class because they are not in same class this is called method overriding.

	// Method overriding
	class Person
	{
		
		display();
	}
	
	class Emp extends Person
	{
		int id,salary;
		public void display()
		{
			super.display();
			syso("ID:-"+id);
			syso("Salary:-"+salary)
		}
	}

Recrusion is calling same method from same method.

	// Recursion
	class Emp extends Person
	{
		public void display()
		{
			display();
		}
	}

The difference between Inheritance and the import in import you cannot access data members of class but in inheritance you can access the data members of super class.

debug,scanner

Scanner

Dynamic Binding

Whenever you create referance of super class you can create object of subclass Person p = new Emp();

If we call p.display(); which display will call, to understand this we need to understand static binding and dynamic binding

static binding (Not used in JAVA)

Binding takes place at compile time
It is based on type of invoking entity
It will resolve on type of p/Person.

Dynmaic binding (used in java)

Binding takes place at run time.
It resolve on type of object refered by invoking entity i.e object of p/Empolyee.
All instance method calls are resolved dynamically so the display() called from empolyee.

	// if you create referance of super class i.e Person p; (Person is super class)
	
	// You can create object of subclass i.e p=new Empolyee(); (Empolyee is subclass)
	
	// you cannot do Empolyee e = new Person();
	
	class Person 
	{
		display()
		{
			System.out.println("Person display");
		}
	}
	
	class Empolyee extends Person
	{
		dislay()
		{
			System.out.println("Empolyee display");
		}
	}
	
	pblic class MainClass
	{
		public static void main(String args)
		{
			//Now see the obj and referance 
			
			Person p = new Empolyee();
			p.display();
			
			// so the question is which display will call Empolyee-> display() or Person-> display();
			
			//java used Dynamic Binding so it called Empolyee display
		}
	}

> The output of the program 
> Empolyee display

Download and see code here

27/5 (class objects, c-o overiding)

Class object

Hierarchy of class object object -> class Person -> class Emp
Super class of Person is object and in object following are the methods
Methods oof class Object
public String toString(); public boolean equals(); public void wait(); public int hashCode(); protected void finalize();
By default this methods are present in every class that you create object.

	p s v m(s [] a)
	{
		Person p = new Emp();
		System.out.println(p);  //p.toString()
		
		//Person class has received toString() from class Object
	}

It will print hash map line office.emps.Emp@262323a

Class object overiding

	// in Person class 
	@override
	public String toString()
	{
		return "Name: "+name+" Birdthdate:- " +bdate;
		
		//name.toString();  bdate.toString();
	}

Output of this code is Name:- shree Birdthday:- utility.Date@5215525a;
To avoid utility.Date@5215525a; on the place of birdthdate you need to write return toString() in Date class.
If there is toString() is in Emp class then it will call Emp -> toString();
In below code Emp class don't contain toString() but its super class contain the toString() so it call Person -> toString();
And for birdthdate the flow is main -> Emp(not toString()) -> Person(super of Emp) -> toString -> Date -> toString();

It represent object in string.
It convert object to string.
Purpose of toString() and display() are the same but toString print directly with the help of object.
Download and see code here

28/5(Multilevel Inheritance,foreach, Abstraction, Access Specificer)

Multilevel Inheritance

The flow of Executing constructor is Person()->Empolyee()->SalesManager()

foreach loop

	Emp [] allemps;
	allemps = new Empolyee[3];
	allemps[0] = new SalesManager();
	allemps[1] = new Admin();
	// Shortcut 
	Empolyee [] allemps = {new SalesManager(), new Admin()};
	
	for (int i=0;i<allemps.length;i++);
	
	// Advanced for loop foreach.
	for(Empolyee e : allemps) 
	{
		System.out.println(e); //e.toString;
	}
	
	// here we achive polymorphism sending same data to every method but every methods acts diffently

foreach is only used for array.
Protected data members are accesssible to its sub classes
If you dont write access specificer then the scope is package
Thre is 4 access specifier public, private, protected and default
keywords are 3 and specificers are 4.

Abstraction

Abstract methods that are not decleared in super class.
Methods that are not decleared are used for polyprism.
If one of the method in the class is decleared as abstract then class should be abstract.
Subclass must to complete abstract method if it fail to complete the abstract method then the subclass will be abstract.
creating instance of abstract class is not allow.
we cannot create object of abstract
non abstract classes are concrate class.
non abstract classes can be decleared as abstract

e.calsal(); will not call because it is not in Super class Emp.

public class Empolyee
{
	public void display()
	{
		System.out.println("Empolyee Display");
	}
	
	
	public void accept()
	{
		System.out.println("Empolyee accept");
	}
}

public class Manager extends Empolyee
{
	display();
	accept();
	calsal();
}

public class SalesPerson extends Empolyee
{
	display();
	accept();
	calsal();
	bonous();
}

public class WageEmp()
{
	display();
	accept();
	calsal();
}

public class MainClass()
{
	Empolyee e = new Manager();
	e.calSale(); //cannot be compile 
	
}

In below code e.calSale(); will not compile because It searches the function in super class i.e in Empolyee.
That is why abstration concept comes in picture.
So you can declear the method in super class but there is no need to declear that method.
You cannot create object of abstract class.
We cannot create object that's why we use array.
Download and see code here

29/5(geter/seter,final,Interface)

geter/seter

The rule says that class data members should be decleared as private.
Because of this its unable to access in subclass.
So there is 2 options to access that data member i.e 1. make it protected so it will accessable to sub class.
And 2nd option is geter and seter methods.
geter() method return private data member.
seter() set new value to private data members.

public class Account
{
	private String name;
	private int no;
}
public String getName()
{
	return name;
}

public String setName(String name)
{
	this.name = name;
	return name;
}

public int getNo()
{
	return no;
}
public int setNo(int no)
{
	this.no=no;
}

final

final is the keyword in java.
It is exactly opposite abstract.
It cannot be modified/change.
it is fully defined.
It can be used in variable,methods and classes.
final is replacement of const in java.
We can only declear final but you have to initilize it afterwords.
fianl variable decleared all in capital i.e final String NAME="shree"
final Methods cannot be overriden.
eg.class object methods wait(),notify(),notifyAll() are defined final.
final classs cannot be modified
String class in java library is decleared as final.
Because you cannot modified final class, fianl class cannot acts as super class.

final keyword for array.

Interfaces

Interfaces are 100% incomplete.
In interface there are abstract methods and concrete methods.
In Inteface there is only final variable and abstract methods (for now)

Multiple interheritance through the classes is not allow but using interface its allow.

Anything you write in interface it will default take public static final

interface Drawable
{
	static double PI = 3.14; //public static and final
	double calArea(); //it can only decleared as public andabstract
	void drawShape(); //methods are bydefault treated as abstract
}

class Rectangle implements Drawable 
{
	privete double lenght,breadth;
	//constractor 
	// here toString method is avalible
	double calArea()
	{
		
	}
	void drawShape()
	{
		
	}	
}

class MainClass
{
	public static void main(String [] args)
	{
	Drawable d = new Circle();
	//interface referance = implementing class instance
	//super class referance = sub class instance
	d.calArea(); // Instance and non static methods resolve using dynamic binding
	//so it will call from the Circle class. 
	}	
}

It has is a relationship.
You cannot create a object but you can create a referance of interface.
You can create only referance of Interface.
There is no any concerete method in interface( upto java 1.7).
Complesary you have to implement all the methods in sub class.

interface A
{
	void m1();
}
interface B extends A
{
	void m2();
}
class X implements B
{
	void m1(){}
	void m2(){}
}

If two interfaces are extend with each others (A and B)
Then in implement class i.e (X) need to implement both interface methods.
Class and Interface relation
- class ---> (extends)---> class
- class ---> (implements)---> interface
- interface ---> (extends)---> interface
Abstract class and Interface cannot create object.
Make difference between class and Interface.
Download and see code here

31/5(typecast, instanceof, interface of java8)

Types of methods

Final Methods
- Final methods are defined final it will not modified/override furtere
Concrete Methods
- In concrete methods we can override or not also.
Abstract Methods
- Abstract methods should be complesary override in subclass
Default Methods
- Default methods are decleared in inheritance onwards java8 as concrete methods in inheritance

How multiple inheritance replaced by interfaces

We can use extend and implement both on one class

public class SalesManager extends Empolyee implement ITraveller
{
	//add all unimplemented methods in ITraveller 
	//ITraveller is interface so you have to implement all methods which in ITraveller
}

typecast

Convert the type of variable/object
double d=4.6; ---> float f=(float)d;

	Empolyee [] allEmp;
	allEmp = new Empolyee[3];
	allEmp[0]=new SalesPerson("",,,,);
	allEmp[1]=new SalesPerson("",,,,);
	allEmp[2]=new SalesPerson("",,,,);
	for (Emp e : allEmp)
	{
		if(e instanceof ITreaveller)	//It checks e can be typecasted toITreaveller so remove error that is showed in typecast
		{
		System.out.println("TA:  "+((ITraveller)e).calculateTA());
		}
	}

instanceof and typecast

instanceof is a operator

It return true and false value
Referance below code and error ---> It checks e can be typecasted toITreaveller so remove error that is showed in typecast
syntax
e instanceof iTreaveller e source, ITreaveller is destination
It avoid error in runtime
It is intelligent way of checking typecast is valid or not
upcasting is not required (super calss methods are avalible for subclass as it is)
Downcast is required (because subclass methods are not avalible in super class)

Extra ↓

It verified calsalary(); is avalible in person or not

Interface onwards java 8

Previously interface only contain abstract methods
If i go and suddenly add abstract method in interface will breakdown existing classes
When this is realize by the oracal and other developers
Now do not add suddenly any abstract method insted of that use default keyword
Also you can add static method in interface
Now there are three type of methods in interface
- Static (not expect to rewrire or overide)
- Abstract (compulsory override)
- default (do or don't)

interface A
{
	void m1();		// compulsory to implement
	default void m2()	// not compulsory use it or not 
	{}
	
	static void m3()
	{
	}

}
class MyClass implements A
{
	void m1(){}
	void m2(){}
}

Interface can be implement across the hierarchy (Not abstract classes)
Interface deside what to do
Class decide how to do it
Download and see code here

1/6

Exception Handling

Handling the error occured during run time
Ther is three type of error
Compilation logical run time
Runtime errors are not under the control of the programmer.
Java library many exception classes are already defined
Exception object are thrown
Expection handling revolves around 5 keywords try catch finally and through

public class ExpectionDemo
{
	public static void main(String [] args)
	{
		try
		{
			int n1= Integer.parseInt(args[0]);
			int n2= Integer.parseInt(args[1]);
			Syso("Division:"+(n1/n2));
		}
		catch(Expection e)
		{
			e.printStackTrace();
		}
	}
}

try-catch
try-catch-catch
try-finally
try-catch-catch-finally

Finally block

Real purpose of finally block is not to handle expection.
Even if there is no expection still finally block always get executed

8/7(Java IO, Stream)

Java IO(Input Output)

Stream is a sequence of data which travelling from source to destination
Stream are in java.io package
Stream
- byte Stream
- Character Stream
  - String, char[]

java io is based on 4 abstract classes
- Byte
- Input Stream
- Output
- character
- Reader
- Writer
Three steps of every IOoperation should be follow
- Open Stream
- Use Stream
- Close Stream
printStream class contain print & println and out is object
In some Stream classes Source and Destination is not defined
eg.ObjectOutputStream
to overcome this will use object chaining
Two stream are together for performing some IO.
FullIOoperation = IO Operation1 + IOoperation2
FileOutputStream+ObjectOutputStream

// Object chaining

Person p = new Person("shree",new DOB(7,8,97));

Consol IO

Predefined Stream
- System.in
- System.out
- System.err
.err/.out/.in <-- are the Static datamembers of System class
.out is object of printstrim class

BufferReader

BufferReader is the character reader stream

Some important functions of BufferReader
br.read()
- It return integer single char
- int i = br.read();
br.readLine()
- It return String
- String str = br.readLine();

// Dummy/psudoCode
BufferReader br = new BufferReader(new inputStreamReader(System.in));   // OPEN STREAM
int n = br.read();							// USE STREAM
System.out.println((char)n);

_______________________________________________________________________

System.out.println("Enter 'q' for exit");
while((n=br.read()) != 'q')						// USE STREAM
{
	System.out.println((char)n);
}
br.close();								// CLOSE STREAM

// Real Code
public static void main(String [] args)
{
	// ISR is passed for creating BR instance is object chaining
	BufferReader br=null;
	try
	{
	 br = new BufferReader(new InputStreamReader(System.in));
	
	syso("Enter q to quit");
	int n;
	
	while(n=br.read())!='q')
	{
		syso((char)n);
	}
	
	}catch(IOException e)
	{
		e.printStackTree();
	}finally
	{
		try{
		br.close();
		}catch{
		
		}
	}

}

BufferReader return type is char so we need to parse a data as follow

Parsing BufferReader

int sid = Integer.parseInt(br.readLine());
String name = br.readLine();
float marks = Float.parseFloat(br.readLine());
double percent = Double.parseDouble(br.readLine());
char ch = br.readLine().charAt(0);

File IO

File Reader

Stream
- FileInput -byte read
- FileReader - char read
- FileOutputStream - byte write
- FileWriter - char write
Creating Stream
It need information of file
We gave info as String path or file object
File object contain metadata (the data about data)
- file size, readable,extra path contain in metadata
There is two way that we can pass the file to file stream
one is direct path
and another is File object

File path

// direct path passing
FileInputStream fis = new FileInputStream("path")
// File object
File f = new File("path");
FileInputStream fis = new FileInputStream(f)

The benifites of passing FileObject is we can use multiple functions in File like
- f.length();
- f.canRead();
- f.isFile();
- f.isDirectory();
- f.lastModified();

// File Reader	

FlieReader fr = new FileReader("path");
int n;
while((n=fr.read()) != -1)  // -1 is end of stream
{
	System.out.println((char)n);
	
}
fr.close();

File Writer

Byte Stream

// Byte Stream Program
public static void main(String [] args)
{
	String s = "github.com/shreeshailaya";
	FileOutputStream fos = null;
	try
	{
		// for rewrite data 
		FOS = new FOS("path");
		// for append data
		FOS = new FOS("path",true);
		byte [] arr = s.getBytes();
		fos.write(arr);		// entire array
		fos.write(arr[0]);	// one byte
		fos..write(arr,0,7);	// first 7 char
		fos.write("\n".getBytes()); // new line
	}
	catch(FileNotFoundExpection ex)
	{
		ex.printStackTree();
	}
	finally
	{
		try catch
		fos.close();
	}
}

Character Stream

// character stream program
public static void main(String [] args)
{
	//for rewrite
	FileWritter fw = new FileWritter("path");
	// for append
	FileWritter fw = new FileWritter("path",true);
	Syso("Enter Data");
	BufferReader br = new BufferReader(new inputStringReader(System.in));
	String s = br.readLine();
	fw.write(s);
	fw.write("\n");
	fw.write(s,0,10);
}

Reading file

class FileReadingDemo
{
	p s v m(String [] args)
	{
		File f = new File("path");
		sysout("Exist: "+f.exist());
		
		if(f.exist() && f.isFile() && f.canRead())
		{
		FileReader fr = new FileReader(f);
		int n;
		while((n=fr.read() != -1))
		{
		
			sysout(n)
		}
		
		}
		fr.close();
	}
	
}

Reading data by Char array

char [] ch = new Char[10];
int n;
while ((n=fr.read(arr)) != -1)
{
	sysout(arr);
}

8/7

Buffered Stream

Buffer is pulling data from file
Buffer is temp memory to file IO
Loding the next data is done by buffered
The purpose of buffered is memory IO and to avoid disk IO
Disk IO is slower are taking time
Same is applicable to write
program first write data in buffered when buffered is full then it will flush the data to file
flushing is occured when buffered is full
Also closing the stream will flush the data
flush() is also used to flush the data to file
Giving the size to buffered is optional you can give with one of constructor
Accouding to stream we need to pass object
Previousely we directly read/write data from hdd now here we read/write data with the help of buffered

//Syntax

BufferedReader brr = new BufferedReader(new FileReader("path"));

BufferedWriter brr = new BufferedWriter(new FileWriter("path"));


BufferedOutputStream bos = new BOS()


int n;
while((n=br.read()) != -1)
{
	sysout((char)n);
}

BufferedWriter bw = new BW(new FileWriter("path"));
bw.write("Some String"); 	//Write on Buffered
bw.newLine();	// new line method
bw.write("Some String");
bw.flush();	// remaining data flush to file
bw.close();

Object IO

Serialzation/ Deserialzation

Saving/writing object state in some perment media like file and DB
Retrive object state in some perment media like file and DB
Streams used for it is
- ObjectOutputStream --> write object/serialization
- ObjectInputStream --> read object/deserialization
We are dealing with object here
We are saving the state of the object in file/db
state are the all instance data members
static data members will discarted here because they are realted with class
No methods i.e behavior
Only set of all instance data members are saved
Some instance data members may be excluded, you can use keyword transient
int empid, date doj, long noOfDays, String name are the state of object
transient is used to not save data, syntax --> transient long noOfDays
Object that is getting Searialized should have serializable implemented
Serialized interfaces are empty they dont contain any methods they are called marker interface it only used for marking the object for serialization
Only Serialized objects can be searized else it will create NotSerializableException
association has a
interface is a
In is a relation do it at the level of super class
In has a relationship do seperately for all component
If implementation of serialization is done for parent class then child class automatically affected
for sealization we us objectOutputStream supported with FileOutput
byte stream are compactable with byte stream character stream is only compactable with char stream
for reading object from file we need OobjectinputStream with FileInputStream
osi.readObject() is the method which read the object or return object
then we have to do down typecast to see the data

	public static void main(String[] args) throws FileNotFoundException, IOException {
		// TODO Auto-generated method stub
		
		Empolyee [] emp = new Empolyee[3];
		
		emp[0]=new Empolyee(1, "shree");
		emp[1]=new Empolyee(2, "shail");
		emp[2]=new Empolyee(3, "Vitkar");
		
		
		ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("/home/shree/Desktop/shree"));
		for(Empolyee e : emp)
		{
			oos.writeObject(e);
		}
		
		System.out.println("Serialization Done");	

	}

// Deserialization

	public static void main(String[] args) throws FileNotFoundException, IOException, ClassNotFoundException {
		// TODO Auto-generated method stub
		
		ObjectInputStream ois = new ObjectInputStream(new FileInputStream("/home/shree/Desktop/shree"));
		
		Empolyee [] emp = new Empolyee[3];
		for (int i=0;i<emp.length;i++)
		{
			//Object o = ois.readObject();
			emp[i]=(Empolyee)ois.readObject();
		}
		
		for(int i=0;i<emp.length;i++)
		{
			System.out.println("Empolyee Name "+emp[i].getName()+"\n Empolyee ID  "+emp[i].getEmpid());
		}

	}

Collection Framework

It gives readymade classes which have implemented a perticular data structure
It is all collection classes will store collection of objects not premetive data types
Collections cannot be of int value but cab be of Integer object
Collection freamework is redesigned after 1.2 v
It is clsses which is acting as datastructure
Classes are bases on set of interfaces
base interface is Collection
there is few methods which are required in all collections like
- add();
- remove();
- size();
- iterator();
Collection is further extended to
- List
- Set
- Queue
Set is further divided into
- SortedSet();
list can consist of duplicates
set is set of unique data
we are going to see classes in interface (list set and queue)

List Interface

Duplicate elements are allowed in list
abstractList is a class
Two important list classes are
- ArrayList
- LinkedList
ArrayList is most used collection
ArrayList can dynamically grow and shrink and workded as array
when there is requirment to search data then we use ArrayList
When there is requirment to add/delete data then we use LinkedList

List l = new ArrayList();
l.add("bakul");
l.add(new Person());

String s = (String)l.get(2); 	// It will genetrate class castclassexception
// we cannoct convert Person object as string

// care has to be taken at the time of adding the element

List <String> l = new ArrayList<>();
// because of <String> i can only pass/add string so there will not need of type cast

is generics which will add type safty to the collection
because of this we can oly add string no need of typecast

//without using generic 

class Demo
{

	//List l = new ArrayList();	//This will generate error
	List <String> l = new ArrayList<>();
	l.add(new String("Welcome"));
	//l.add(new Date());
	//l.add(new Integer(45));
	
	//String s = (String)l.get(1);
	// String s = l.get(0);
	
	Sysout(l); //call toString print all elements
	
	l.add(2,"xyz"); //addded to index 2
	l.remove(3);	//remove element
	l.remove("xyz"); // remove by value
	
	
	// advanced loop
	for( String s : 1)
		sysout(s.toUpperCase());
}

9/7(Collections)

Utility Classes

It is collection of objects
You can add any object to collection
Base of collection is lies on set interface
Collections is interface has some methods add,remove..etc
Collections is extended to List, Set and Queue
In list duplicate are allow

Iterator method for ittration data from collection

**** // Collection upto Reversion

Collection freame work

Types of collections classes
- List
  - al
  - ll
- set
  - hs
  - ts
- queue
  - pq
adding, removing, Itreating
common algos Collections (class with static methods)
Map key value map --> set
lagecy classes
- stack

10/7

Iterating

We can iterate data from three ways from collections
- Advanced for loop
- using iterator
- List Iterator(only for list)
Advanced for loop

set<String> str = new ArrayList<>();

for(String s : str)
{
	syso(s);
}

using iterator
Iterator has two methods as follow
- has()
- hasNext()

List<String> str = new ArrayList<>();
Iterator i  = str.iterator();
while(hasNext())
{
	syso((String)next());
}

ListIterator
ListIterator has three methods as follow
- next()
- hasNext()
- hasPrevious()

List<String> str = new ArrayList<>();
ListIterator<String> li = str.listIterator();
while(li.hasNext())
	li.next();
	
while(li.hasPrevious())
	sysout(li.previous());

HashSet

Hashing is the storing a data in a perticular way
In

13/7

Multithreading

What is thread? Compare thread process?
why mltithread application
thread life cycle
creating a simple thread
There is two different way to creating thread
- extends Thread (Class)
- implement runnable (Interface)
Thread
Specific to the task
- run()
control the task
- start()
- join()
- Sleep()
In runnable it has only on method that is run();

Create a thread

//syntax

class MyThread extends Thread
{

	p v run()
	{
		//specify the task
	}
}

class ThreadApp
{

	p s v m();
	{
		Thread t = new MyThread();	//newly created state
		t.start();	 // before call run you have to call start()
		// when you call start() then it will automically call run() from MyThread class
		
		 
	
	}
}





// Implement Runnable 
class MyTask implements Runnable
{
	pv run()
	{
		//specify task
	
	}

}

class ThreadApp
{

	main()
	{
		Runnabble r = new MyTask();
		Thread t = new Thread(r);	//newly created state
		t.start();	// call run()
		
		// we are indirect calling the start by thread 
		// Runnable is always depend on thread
	}

}

Runnable is always depend on thread

class MyThread extends Thread
{

	public void run()	//task to be done by the thread
	{
		for(int i =1;i<=5;i++)
		{
			sysout("child Thread"+i);

			try
			{
			Thread.sleep(500);	//sleep is static method
			// we cannot handle throws exception here 
			}
			catch (InterruptedException e)
			{
				e.printStackTree();
			}

		}
	}

}


main()
{

Thread t = new MyThread();
t.start

for(int i=1;i<=5;i++)
{


}

}

// Runnable
main()
{
	// represent task
	Runnable r = new MyTask();
	Thread t = new Thread(r);
}

Threasd Synchronization

Because of Multiple thread we achive better performancw
when multiple thread share common resource (object) it may lead to data inconsistancy
Thread Sync is needed when multiple thread share common resource (Object)
Because of every thread is giving some time so it not able to complet its task
So 1st thread will lock object
others process will go to waiting because object is locked
and when 1st complete the task then it will unlocak
Best example is ATM
Here is the dealy of time but we are achiving here data consistency
Synchronised keyword is used to locking the object
you can use sync keyword on block of code or method

what why where

Concept

What

Why

Where

Comment

Referance

Java

Programming language

For building applications(web,mobile)

All over industry

It is a programming language based on OOP's concepts

Notes, official docs

JVM

Java Virtual Machine

Running Java

Installed in system for running java

To allow Java programs to run on any device or operating system (known as the "Write once, run anywhere" principle), and to manage and optimize program memory

Infoworld

JDK

Java Development Kit

Required by developers for developing and testing the application

In development enviroment

Notes, Java docs

JRE

Java Runtime Environment

It is needed by client machine to run existing java application (already compiled)

In development enviroment

Notes

OOP