command line arguments for a file

[deepika deepi]

i have an file to read and i have given the file name inside the FileInputStream and i want to give the file name during run time like this

compile
javac FileRead.java
run
java FileRead 1.txt and the contents inside the file should be displayed

the coding is

import java.io.*;
class FileRead 
{
 public static void main(String args[])
 //public static String getContents(File aFile) 
	{
 //   StringBuilder contents = new StringBuilder();

      try{
		// Open the file that is the first 
		// command line parameter
		FileInputStream fstream = new FileInputStream("1.txt");
		// Get the object of DataInputStream
		DataInputStream in = new DataInputStream(fstream);
        BufferedReader br = new BufferedReader(new InputStreamReader(in));
      //BufferedReader input =  new BufferedReader(new FileReader(aFile));

		String strLine = null;
		//Read File Line By Line
		while ((strLine = br.readLine()) != null) 	{
			// Print the content on the console
			System.out.println (strLine);
		}
		//Close the input stream
		in.close();

		}catch (Exception e){//Catch exception if any
			System.err.println("Error: " + e.getMessage());
		}
}
	}

what are all the necessary changes to be made for giving the input text file name during run time?

[Campbell Ritchie]

You can create a prompt to request a file name. You can use a file chooser. Lots of ways to do it.

[Jesper de Jong]

The code on line 12 is not doing what the comment on lines 10 and 11 say.

The args array that is passed to the main method (line 4) contains the command line parameters.

[deepika deepi]

ya.. but how to use those arguments in the coding instead of giving the file name instead?

[Campbell Ritchie]

Line this?

[deepika deepi]

i'm getting an error like this for the code what i'm using
error

import java.io.*;
class FileRead 
{
 public static void main(String[] args)
 //public static String getContents(File aFile) 
	{
   StringBuilder contents = new StringBuilder();

      try{
		// Open the file that is the first 
		// command line parameter
	{
		
		FileInputStream fstream = new FileInputStream("System.in");
		// Get the object of DataInputStream
		DataInputStream in = new DataInputStream(fstream);
        BufferedReader br = new BufferedReader(new InputStreamReader(in));
      //BufferedReader input =  new BufferedReader(new FileReader(aFile));

		 for(String strLine:args)
{
		//Read File Line By Line
		while ((strLine = br.readLine()) != null) 	{
			// Print the content on the console
			System.out.println (strLine);
		}
		//Close the input stream
		in.close();

		}catch (Exception e){//Catch exception if any
			System.err.println("Error: " + e.getMessage());
		}
}
	}
}
//}

can you tell why i'm getting this error?

[deepika deepi]

can any one make my code reor free and get the output in the file? or can you send an error free code for java?please any one help me

[Campbell Ritchie]

deepika deepi wrote:can any one make my code reor free and get the output in the file? or can you send an error free code for java?

No. That’s not how we work.

deepika deepi wrote:please any one help me

We are trying to help you. You asked how to get the file name from the command line and I sent you a link. Did you read it? You didn’t tell us what error you are suffering.

[Jesper de Jong]

Please ShowSomeEffort.

Did you click the link that Campbell posted? The tutorial shows very clearly how to use the command line arguments.

Look at line 14 of your code. You're not using the command line arguments here.

// Tries to open a file named "System.in". That's not what you want.
FileInputStream fstream = new FileInputStream("System.in");

The command line arguments are what is passed to the main method in the args array.

public static void main(String[] args) {    // <= Right there! args contains the command line arguments.

So, what do you think you need to change in line 14 so that the program is going to use the first command line argument there?