Basic File Handling in Java - Part 2

In the previous article, we discussed about two basic file handling functions in Java including searching for an existing created file in the system and creating a file using java’s inbuilt function.

In this article we will cover up the other two file handling operations which includes reading from a file and writing to a file using java’s own methods. In this program we create a file by specifying a file name, open it at the same time and add records to it as per custom format. After writing to the file, it is good practice to close it.

import java.io.*;

import java.lang.*;

import java.util.*;

public class FileHandlingTrial {

       private Formatter file;

      

              public void openFile (){ //creating & opening a file

                    

                     try{

                           file= new Formatter("New Text Document.txt"); //will be created in default workspace folder else specify a path

                     }

                    

                     catch(Exception e){

                           System.out.println("Illegal file operation");

                                 

                           }

                     }

                    

                     public void addRecords(){// writes to the created file

                           file.format("%s %s %s", "99", "MCA", "IP University");

                    

                     }

                    

                     public void closeFile(){ //good practice to close the file after use

                           file.close();

                     }

      

}

class FileHandlingTrial1 {

      

       public static void main(String[] args){

             

         FileHandlingTrial asp = new FileHandlingTrial();

        

         asp.openFile();

         asp.addRecords();

         asp.closeFile();

             

       }

}

In this last program of file handling we will read the content added by the user.

Here also we create three methods in which first opens the file, second reads the content of the file and third one finally closes the file after reading the contents.

import java.io.*;

import java.util.*;

public class FileHandlingTrial {

private Scanner file;

public void openFile(){ // to open the file

      

       try{

              file = new Scanner(new File("new.txt"));

             

             

       }

      

       catch(Exception e){

             

              System.out.println("File not found");

       }

}

public void readFile(){ // to read data from the file

      

       while(file.hasNext()){

              String a=file.next();

              String b=file.next();

              String c=file.next();

              String d=file.next();

             

              System.out.printf("%s %s %s %s\n", a, b, c, d);

             

}

}

public void closeFile(){

file.close();

}

}

class FileHandlingTrial1 {

      

       public static void main(String[] args){

             

         FileHandlingTrial asp = new FileHandlingTrial();

        

         asp.openFile();

         asp.readFile();

         asp.closeFile();

             

       }

}

Screenshot // click to open a higher resolution version

Basic File Handling in Java – Part 1

Java provides File class in ‘java.io’ package for handling all basic and necessary file operations and methods used for file handling like reading the contents of a file, writing to a file, searching for a file, determining the path of the file stored on a disk, etc. File class contains number of methods for performing specific operations on a file, few of which are used in this article.

In this program, the user is checking for the existence of a particular file stored on system’s hard disk. File class of Java IO package has been used to provide access to methods like exists(), getName() which checks for the file and if found returns the message else gives user defined message.

import java.io.File; //file class for basic file operations

class FileHandlingTrial{

               

         public static void main(String[] args) {

                               

  File asp = new File("C:\\file\\info.txt"); // constructor takes the path of the file already existing on the system

                               

             if(asp.exists()) // built in method to test whether a specified file exists or not.

                                               

                        System.out.println(asp.getName() + "File Found"); // prints the message along with file name

                                               

                                        else

                        System.out.println("File Not Found");

                               

                }

}

In the previous program we checked for an already created file on the system. We can also create a file using the program with help of facilities provided by java.io package

import java.util.*;

class FileHandlingTrial{

               

                public static void main(String[] args) {

                               

                                final Formatter asp; //formatter print strings to file

                               

                                try{

                                      asp = new Formatter("c://file//trial.txt"); //provide path of file where it will be stored

                                               

                                                System.out.println("File Created");

                                }

                               

                                catch(Exception e){

                                               

                             System.out.println("Error"); // for possible mistyping of wrong or illegal folder location like specifying a drive which does not exist on system.

                                }

                                               

                }

}

In the next article which will be part 2 of file handling, reading from a file and writing to a file will be discussed. Thanks folks for reading. 

Screenshot // click to open a higher resolution version

Exception Handling Basics in Java

Exception handling in java is similar as in C#. There are couple of differences like java allows checked exceptions which are handled by the caller of the program. Another minor difference is in the finally statement which can have return and break statement which is not the case in C#.

Refer to previous article for Introduction to Exception handling Exception Handling Basics in C#

Following code illustrates the basic concept of exception handling dealing with divide by zero exception in Java. As we know exception is any abnormal condition in a program which abrupt the normal flow of the program. Exception handling allows users to take corrective measures and have easy to understand information returned to them in case an exception arises.

import java.util.*;

public class ExceptionTrial {

               

                public static void main(String[] args){

                Scanner input = new Scanner(System.in); //allows the user to input values

               

                int x=1;

               

                do{

               

                try{ //put the code in try block which may raise an exception

                               

               

                System.out.println("Enter a number  :");

                int n1=input.nextInt();

                System.out.println("Enter another number to divide");

                int n2=input.nextInt();

                int sum = n1/n2;

               

                System.out.println(sum);

                x=2;

                }

               

                catch(Exception e){   //handles the exception, lets the user know whats wrong.

                               

                                System.out.println("You can not divide a number by zero");

                               

                }

                }while(x==1); // loop to let user enter correct value after encountering exception

               

               

                }

            

}

Screenshot // click to open a higher resolution version

Exception Handling Basics in C#

An exception is any uncommon condition arising during execution of a program. There might be several conditions when an exception is encountered in a program but at most basic level examples of exceptions include file not found exception, dividing a number by 0, inputting a wrong data type values etc

It is necessary to handle exceptions otherwise an end user will not feel at home with the application and it is a sign of poor problem understanding. Just for example, if there is a program which accepts a string “thinkdigital” and converts it to uppercase “THINKDIGITAL” and vice a versa then there must be a facility which handles an event when a user enters a non-string input which cannot be understood by the program. This is just an example to make any layman understand about the logic of exception

In .net framework, we have System.Exception class which provides all possible exception handling facility in c#.

Any piece of code which can trigger an exception goes under the ‘try’ block, once an exception occurs, the control moves to the ‘catch’ block and handles the exception. A try block can have number of catch block depending upon different types of exceptions occurring during an operation. But always the base catch block executes first and if required child catch blocks are executed.  There is a ‘finally’ block which is optionally used for performing maintenance tasks like freeing memory, closing file stream connections etc.


// Illustration code

using System;
using System.IO; //required for file operations


class ExceptionExampleProgram
{
    public static void Main()
    {
        StreamReader streamReader = null;
        try //code which may trigger an exception comes under the try block
        {
            streamReader = new StreamReader("C:\\file\\info.txt"); //reads the content of the file specified
            Console.WriteLine(streamReader.ReadToEnd());
            streamReader.Close();

        }
        catch (FileNotFoundException Trial) // handles the exception using predefined properties in exception class or user defined message
        {

            //Console.WriteLine(FileNotFound.Message); // printing message using system defined 'Message' property
            Console.WriteLine("This program can not find the file specified {0}, Please check again", Trial.FileName); // printing user defined message to make things more clear
         
        }
        finally // to perform clean up tasks like closing connections and release memory for efficiency
        {
            if (streamReader !=null) // required as if stream reader is null then it cant be closed
            {
            streamReader.Close();
            }
            Console.WriteLine("Stream reader now closed, so is this article :P");
            Console.ReadLine();
        }
    }
}

Screenshots // click to open a higher resolution version

/* Normal Execution */

/* File Not Found Exception Handling */

/* Another type of exception which can occur if directory path is altered, 

another catch block is required for this */