1) Java Introduction
2) Data Types
3) Variables
4) Operators
5) Control Statements
6) Arrays
7) String, String Buffer, StringBuilder
8) Command Line Arguments
9) Classes
10) Objects
11) Variables (non-static, static & local)
12) Methods ( method params & method return types)
13) Constructors
14) Blocks ( IB and SB)
15) Encapsulation
16) Inheritence
17) Polymorphism
18) Method Overloading
19) Method Overriding
20) Abstraction
21) Interfaces
22) Abstract Classes
23) Marker Interfaces
24) Variable Arguments
25) static keyword
26) this keyword
27) super keyword
28) final keyword
29) java.lang.Object class & method
30) Wrapper Classes
31) Type Casting
32) Packages
33) static import
34) Exception Handling
35) try-catch-finally- throws-throw
36) Exceptions Hierarchy
37) Checked Exceptions
38) Un-Checked Exceptions






1) File Handling
2) Multi-Threading
3) Collections
4) Generics
5) Inner Classes
6) Reflection API
7) Garbage Collection
8) Java 1.8 features



============
File Handling
===========

-> File Handling is Very important area in every programming language

-> Below are the common file operations in the project

1) Create a file
2) Write the data to file
3) Read the data from file
4) Delete the file

-> To perform File operations java language provided one predefined class java.io.File

-> java.io package contains set of classes & interfaces to perform input and output operations

			File  f = new File (String name);

			File f1 = new File (File parent, String child ) ; 

-> We have several methods in the file class

boolean createNewFile ( ) : It is used to create a new empty file

boolean mkdir ( ) : It is used to create new empty directory

String[ ]  list ( ) : It is used to read the content of the given path

boolean delete  ( ) : It is used  to delete the file / directory based on given name

isFile ( ) : To check weather it is a file or not

isDirectory ( ) : To check weather it is a directory or not


import java.io.File;
import java.io.IOException;

public class Demo {

	public static void main(String... args) throws IOException {
			
			File  f = new File("ashokit.txt");
			boolean fstatus = f.createNewFile ( );
			System.out.println(fstatus);

			File f1 = new File("java.txt");
			boolean f1status = f1.createNewFile ( );
			System.out.println(f1status);

			File f2 = new File("mywork");
			boolean f2status = f2.mkdir( );
			System.out.println(f2status);

			File f3 = new File("data");
			f3.mkdir ( );

			File f4 = new File(f3, "test.txt");
			f4.createNewFile ( );
	}

}





// Java program to display all the files and directories in given path


import java.io.File;
import java.io.IOException;

public class Demo {

	public static void main(String... args) throws IOException {
			
			File f = new File ("C:\\Users\\ashok\\classes\\19-JRTP");

			String [ ]  arr = f.list ( );

			for ( String name : arr) {
				System.out.println (name);
			}
	}

}

Assignment : Write a java program to display content of given directory.
For filename it should display prefix as File : 
For directory name it should display prefix as Directory :

Ex:

File : abx.txt
File: demo.txt
Directory: one
Directory: two


package in.ashokit;

import java.io.File;
import java.io.IOException;

public class Demo {

	public static void main(String... args) throws IOException {

		File f = new File("C:\\Users\\ashok\\classes\\19-JRTP");

		String[] arr = f.list();

		for (String name : arr) {

			File f1 = new File(f, name);

			if (f1.isFile()) {
				System.out.println("File :: " + name);
			}

			if (f1.isDirectory()) {
				System.out.println("Directory  :: " + name);
			}
		}
	}
}

===============
IO Streams
===============

-> To perform operations on the file we need to use I/O Streams.

-> Using I/O streams we can establish link between java program and file (physical file )
				
								  write
				java program <--------------------> file

									read
				java program <-----------------------> file


-> IO streams are divided into 2 types

			1) Byte Stream   : To read/write binary data (images, audios, videos, pdfs etc...)					

			2) Character Stream : To read/write character data ( text files )


-> Byte Stream providing 2 types of classes

				1) Input Stream Related Classes ( Ex: FileInputStream )
				2) Ouput Stream realted classes  (Ex: FileOuputStream )

-> Character Stream providing 2 types of classes

				1) Reader classes  ( Ex: FileReader )
				2) Writer classes	(Ex: FileWriter )


// Java Program to write the data to a file using FileWriter class
import java.io.*;

public class Demo {

	public static void main(String... args) throws IOException {		

			FileWriter  fw = new FileWriter("data.txt");

				fw.write("Hi, good evening");

				fw.write("\n");  // it represents new line

				fw.write("How are you?");

				fw.flush ( );

				fw.close( ) ;
	}

}


// Java program to read file data using FileReader class

import java.io.*;

public class Demo {

	public static void main(String... args) throws IOException {		

		FileReader fr = new FileReader ("data.txt");
		int  i = fr.read ( );

		while ( i != -1 ){
			System.out.print( (char) i );
			i = fr.read ( );	// read next character and re-initialize i var
		}
		fr.close ( );
	}

}


// Java Program to read file data using BufferedReader

import java.io.*;

public class Demo {

	public static void main(String... args) throws IOException {			

		FileReader fr = new FileReader("data.txt");

		BufferedReader br = new BufferedReader(fr);

		String line = br.readLine ( ); // reading first line data

		while ( line != null ) {
			System.out.println( line );		
			line = br.readLine ( ) ; // reading next line and re-initialzing line variable
		}		
	}
}



Note: FileReader will read the data character by character where as BufferedReader will read the data Line by Line.


*File Handling Assignments :*

1) Write a java program to find how many characters, how many words and how many lines available in the file

2) Write a java program to read 2 files data and write 2 files content into 3rd file.

3) Write a java program to find names which are available in 2 files.

==========
PrintWriter
==========

				System.out.println ("hi");

				System ----> It is a class available in java.lang package

				out  ---> it is a static variable available in System class.
						  The data type of 'out' variable is PrintWriter class

				println ( ) ---> it is a method available in PrintWriter class



// Writing data to console using PrintWriter object

package in.ashokit;

import java.io.PrintWriter;

public class Demo {

	public static void main(String[] args) {
		PrintWriter pw = new PrintWriter(System.out);
		pw.print("hi");
		pw.println("hello");

		pw.flush();
		pw.close();
	}
}


// Writing data to file using PrintWriter object

package in.ashokit;

import java.io.PrintWriter;

public class Demo {

	public static void main(String[] args) throws Exception {
		PrintWriter pw = new PrintWriter("f1.txt");
		pw.write("this is my f1 file data");
		pw.flush();
		pw.close();

	}
}





1) File 
2) File class methods
3) FileWriter
4) FileReader
5) BufferedReader
6) PrintWriter



==========================
Serialization & De-Serialization
==========================

-> When we store data in the object, that data will be available if our program is running. If our program got terminated then we will loose our objects and data available in the objects.

-> If we don't want to loose the data even after program got terminated then we should go for Serialization.

-> The process of converting java object into file data in the form of bits and bytes is called as Serialization.

-> The process of converting file data back to java object is called De-Serialization.


Note: To perform Serialization & De-Serialization we have to implement java.io.Serializable interface which is marker interface


// Java program on Serialization & De-Serialization

package in.ashokit;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

public class Person implements Serializable {

	/**
	 * 
	 */
	private static final long serialVersionUID = -100l;

	int id;
	String name;

	public static void main(String[] args) throws Exception {

		Person p = new Person();
		p.id = 100;
		p.name = "Raju";

		System.out.println("====Serialization Started ========");

		FileOutputStream fos = new FileOutputStream("person.ser");
		ObjectOutputStream oos = new ObjectOutputStream(fos);
		oos.writeObject(p);
		oos.flush();
		oos.close();
		System.out.println("====Serialization completed========");

		System.out.println("==========De-Serialization Started==========");

		FileInputStream fis = new FileInputStream("person.ser");
		ObjectInputStream ois = new ObjectInputStream(fis);
		Object object = ois.readObject();
		Person p1 = (Person) object;
		System.out.println("Id : " + p1.id);
		System.out.println("Name : " + p1.name);
		ois.close();

		System.out.println("==========De-Serialization Ended==========");

	}

}

========================
What is SerialVersionUID ?
========================

-> For every .class file JVM will assign one random number that is called as serialVersionUID.

-> When we serialize the object, JVM will assign .class file serialVersionUID to serialized file

-> When we de-serialize JVM will compare serialized file UID and .class file UID. If both ids are matching then only de-serialization will happen otherwise it will throw INvalidClassException.

-> To overcome this problem we can write our own serialVersionUID then jvm will not assign that.




================
transient keyword
================

-> If we have any sensitive / secret data then we shouldn't serialize those fileds.

-> transient keyword is used to ignore variables from serialization process



public class Person implements Serializable {

	/**
	 * 
	 */
	private static final long serialVersionUID = -100l;

	int id;
	String name;
	String email;
	transient String pwd;

}


Note: If we serialize the above person class object, id, name and email will be serialized and pwd will not get serialized because it is transient variable.





package in.ashokit;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

public class Person implements Serializable {

	/**
	 * 
	 */
	private static final long serialVersionUID = -100l;

	int id;
	String name;
	String email;
	transient String pwd;

	public static void main(String[] args) throws Exception {

		Person p = new Person();
		p.id = 100;
		p.name = "Raju";
		p.email = "raju@gmail.com";
		p.pwd = "raj@123";

		System.out.println("====Serialization Started ========");

		FileOutputStream fos = new FileOutputStream("person.ser");
		ObjectOutputStream oos = new ObjectOutputStream(fos);
		oos.writeObject(p);
		oos.flush();
		oos.close();
		System.out.println("====Serialization completed========");

		System.out.println("==========De-Serialization Started==========");

		FileInputStream fis = new FileInputStream("person.ser");
		ObjectInputStream ois = new ObjectInputStream(fis);
		Object object = ois.readObject();
		Person p1 = (Person) object;
		System.out.println("Id : " + p1.id);
		System.out.println("Name : " + p1.name);
		System.out.println("Email : " + p1.email);
		System.out.println("Pwd : " + p1.pwd);
		ois.close();

		System.out.println("==========De-Serialization Ended==========");

	}

}