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java redirection

Timothy Leong
Ranch Hand

Joined: May 25, 2005
Posts: 55
hi guys,

my program require user to read in file using the following command

1) java test < input.txt

or using this

2)
java test
Enter your filename: input.txt


I only able to do the first 1. I am using
Scanner input = new Scanner(System.in);

how do the program detect there is not file redirection and display the second option instead?
i tried input.hasNext() however it cannot work. Thank you
Michael Ernest
High Plains Drifter
Sheriff

Joined: Oct 25, 2000
Posts: 7292

What does input.hasNext() return when no file has been redirected to the program?


Make visible what, without you, might perhaps never have been seen.
- Robert Bresson
Timothy Leong
Ranch Hand

Joined: May 25, 2005
Posts: 55
how should i detect there is no file?
Michael Ernest
High Plains Drifter
Sheriff

Joined: Oct 25, 2000
Posts: 7292

You don't need to. If a file has been redirected to your program and there's stuff in it, then System.in will have a handle it. If there's nothing in the System.in buffer, then you can assume no file has been passed to you.
Timothy Leong
Ranch Hand

Joined: May 25, 2005
Posts: 55
I wan to design my program in the way that
user can use redirection to read in file

java program < input.txt

if the user enter command java program,
the program will display "Enter file name:"
from there, the user will key in the file name.

how do System.in detect there's no file redirection instead?

Thank you
Ernest Friedman-Hill
author and iconoclast
Marshal

Joined: Jul 08, 2003
Posts: 24187
    
  34

It doesn't matter. Just write the program as if there's someone there typing. If input is coming from a pipe instead, then the prompts will be printed, but no-one will read them. They'll just be ignored.


[Jess in Action][AskingGoodQuestions]
Timothy Leong
Ranch Hand

Joined: May 25, 2005
Posts: 55
Hi, I tried just the following code but do not work.
I would like the program to skip the User input if file redirection is used. or skip file redirection and request for user input if command "java program" is used.

 
I agree. Here's the link: http://aspose.com/file-tools
 
subject: java redirection