Java Program to Read a File

How to read input file in Java program?

FileInputStream is most often used stream class to read the file in java.

How to use FileInputStream class?

FileInputStream(String fileName) throws FileNotFoundException

here fileName specifies the name of the file that we want to read in java program.

When FileNotFoundException exception is thrown in java program?

FileNotFoundException is thrown when creating an input stream object if file does not exist.

Is there need to close InputStream object?

Yes, We have to close the InputStream object using close() method Once file reading is done.

void close() throws IOException

To read a file, read method is available in InputStream object.

int read() throws IOException

//Java code to read from file using FileInputStream class                       
import java.io.*;                                                               
                                                                                
class FileReadTest {                                                            
 public static void main(String args[]) throws IOException {                    
  FileInputStream fin;                                                          
  try {                                                                         
   fin = new FileInputStream(args[0]);                                          
  } catch(FileNotFoundException ex) {                                           
    System.out.println("File is not found: "+ args[0] + ", error: " + ex.toString());
    return;                                                                     
  } catch(ArrayIndexOutOfBoundsException ex) {                                  
    System.out.println("Error: "+ ex.toString());                               
    return;                                                                     
  }                                                                             
  int byteval;                                                                  
  // Reading file content and prints in console output.                          
  while(true) {                                                                 
   byteval = fin.read();                                                        
   //stops loop when reading value -1 which is the end of file character.       
   if(byteval == -1)                                                            
    break;                                                                      
   System.out.print((char) byteval);                                            
  }                                                                             
                                                                                
  fin.close();                                                                  
 }                                                                              
}   

Output:

$ javac FileReadTest.java 
$ java FileReadTest input.txt
# Reading Input for java program
--------------------------------
Reading line1
Reading line2
Reading line3
-------------------------------

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