File Handling

 File- 

file is a location in a computer system where the information is stored.

Types of file-

1. System file - exe files(run by the system)

2. User file - txt,.java,.c (all user defined files) 

File handling- manipulation with the file like creation, updation, deletion or etc.

Two properties of file-

1. Name

2. Extension

Works on two methods- 

1. file will be created.

2. it is already existed.

How to create a file- 

step 1: we have to include a package to create a file.

import java.io.File;

step 2: Create an object of File.

File f1 = new File();

step 3: pass the name of file in the parameter.

File f1 = new File("Hi.txt");

step 4: check wheather the file will be created or already existed using createNewFile().

step 5: Put the whole program inside try catch block. Inorder to catch the Exception we have to include - 

import java.io.*;

(*- symbolises all utilities)

Program -

import java.io.File;

import java.io.*;

public class app

{ 

public static void main(String args[]) 

{  

try

{

 File fo1 = new File("Hi.txt"); 

 if(fo1.createNewFile()) 

 {

 System.out.println("file is created");

 } 

 else

 {

 System.out.println("Already exists");

 }

} 

catch(Exception e) 

{

} 

}

}

 

How to write in a file- 

step 1: create an object of FileWriter, pass the file name in the argument.

FileWriter fo1 = new FileWriter("Hi.txt");

step 2: pass what you want to write in a file inside the write() 

fo1.write("This is my first file"); 

step 3: After writing we have to close the Writer

fo1.close();

Program- 

import java.io.File;

import java.io.*;

public class app

{ 

public static void main(String args[]) 

{  

try

{

 FileWriter fo1 = new FileWriter("Hi.txt"); 

 fo1.write("This is my file");

 fo1.close();

} 

catch(Exception e) 

{

} 

}

}

How to read the file-

step 1: create an object of File.

File fo1 = new File("Hi.txt");

step 2: Create an Scanner's object.

Scanner s1 = new Scanner();

step 3: Pass the File's Object in Scanner's argument

Scanner s1 = new Scanner(fo1); 

Scanner is used to read the file.

step 4: while loop is used to read till the End Of File

while()

{

}

 

step 5: In while loop's condition use hasNextLine() 

while(s1.hasNextLine()) 

{

}

hasNextLine() checks the next line in the file.

step 6: Inside the while loop 

while(s1.hasNextLine()) 

{

String data = s1.nextLine();

System.out.println(data);

}

nextLine() is used to read the data.