Java Program for Writing a file

How to write a file in java program?

FileOutputStream is most often used stream class to write a file in java.

How to use FileOutputStream class in Java program?

FileOutputStream(String fileName) throws FileNotFoundException

here fileName specifies the name of the file that we want to write in java program.
FileNotFoundException is thrown when creating an input stream object if file does not exist.
Once file reading is done, need to close the input stream object using close() method.

void close() throws IOException

To write a file, write method is available in FileOutputStream object.

void write(int byteval) throws IOException

How to copy a file in java program?

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

Output:

$ javac FileCopyTest.java 
$ java FileCopyTest input.txt input1.txt

// input1.txt file is created with same input.txt file content
# Reading Input for java program
--------------------------------
Reading line1
Reading line2
Reading line3
-------------------------------

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