Take input at program execution

Question

I am looking at starting a program on the command line as normal. (i.e java myprogram)

However I know it's possible to type

  java myprogram configfile.txt

so it takes this string and later on in the code I can use it to load a file.

How do I capture this input in the program using something like a constructor if possible.

Have you searched at all for getting Java command line input? — Dave Newton, Nov 24 '14 at 22:44
possible duplicate of [Java Command line arguments](http://stackoverflow.com/questions/716153/java-command-line-arguments) — Joseph Dailey, Nov 24 '14 at 22:49

takendarkk · Accepted Answer · 2014-11-24T23:11:35.660

4

public static void main(String[] args) { ... }

args array contains the parameters from the command line. In your example the filename would be args[0]. Beware however that if you hard code args[0] into your code, then don't pass a parameter, you will get an ArrayIndexOutOfBoundsException because args[0] doesn't exist.

You can expand this to include multiple parameters if you need to. For example

java myprogram configfile.txt configfile2.txt configfile3.txt

Those filenames would be args[0] args[1] and args[2] respectively.

If your program can run with or without arguments, you can find out if you have some by checking the length of the array is > 0. Something like

if (args.length > 0) { myfile = args[0]; }
else { myFile = someDefaultFilename; }

or if you can have multiple parameters you can loop through the entire array

for (String s : args) { //Do something with each parameter }

edited Nov 24 '14 at 23:11

answered Nov 24 '14 at 22:44

takendarkk

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Thanks for watchin my back. – takendarkk Nov 24 '14 at 22:49
How would I do the code to check if an argument was passed? If doing an if statement it throws this exception if (args[0]!=null){ filename = args[0]; } – chostwales Nov 24 '14 at 22:59
I will add it to the answer. – takendarkk Nov 24 '14 at 23:01
2

@chostwales `if (args.length == x)` with `x` as the expected size. – Tom Nov 24 '14 at 23:02
You don't have to check the size of `args` if you use a `for each` loop. `args` won't be `null` and if it is empty, then this loop will be skipped without any problem. – Tom Nov 24 '14 at 23:10
I need to pass some of my rep from this answer to you :) – takendarkk Nov 24 '14 at 23:11
You can create an `1,000` bounty question and I'll answer it :P. Just kidding. You're welcome :). – Tom Nov 24 '14 at 23:13
You changed "your" to "you're". You officially rock. – takendarkk Nov 24 '14 at 23:23

Take input at program execution

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