[FIXED] Inputting file name through main function argument (args[0])

Issue

EDIT: to run my code i am using "java filename.java input1.txt" is this correct?

I am creating a program where i have to tokenize a string into separate words and that string is in a text file. I have to specify the text file name in the terminal through command line arguments (args[0], etc). I am able to scan and print the content of the text file if i specify through paths but when i try to do it using args[0] it doesn't seem to work. I am using net beans. I will attach my section of code here:

public static void main(String[] args) {   
    try {
        File f = new File(args[0]);   
        //using this commented out section using paths works File f = new 
        //File("NetBeansProjects/SentenceUtils/src/input1.txt");
        Scanner input = new Scanner(new FileInputStream(f));

        while(input.hasNext()) {
            String s = input.next();
            System.out.println(s);
        }
    } catch(FileNotFoundException fnfe) {
        System.out.println("File not found");
    }

    SentenceUtils s = new SentenceUtils();
}

Solution

java filename.java input1.txt

is not correct for running a java program, you need to compile the *.java file to get a *.class file which you can then run like:

java filename input1.txt

assuming your class is in the default package and you are running the command in the output directory of your compile command, or using the fully qualified class name of the class, i.e. including the package name. For example if your class is in the package foo/bar/baz (sub folders in your source folder) and has the package declaration package foo.bar.baz;, then you need to specify your class like this:

java [-cp  your-classpath] foo.bar.baz.filename input1.txt

for input1.txt to be found it has to be in the same directory where you run the command.

your-classpath is a list of directories separated by a system dependent delimiter (; for windows, : for linux, ...) or archives which the java command uses to look up the class to run specified and its dependencies.

NetBeansProjects/SentenceUtils/src/input1.txt is a relative path.

File f = new File("NetBeansProjects/SentenceUtils/src/input1.txt");

if this works then it means that the current working directory (i.e. the directory from which all relative paths are calculated) is the the rectory named NetBeansProjects.

You get FileNotFoundException because your file is expected to be in

NetBeansProjects/input1.txt

To find out which is the current working directory for your running program you can add the following statement:

System.out.println(new File("").getAbsolutePath());

Place input.txt in that directory and it will be found.

Alternatively you can pass the absolute path of your input file. an absolute path is a path that can be used to locate your file from whatever location your program is running from on your local filesystem. For example:

    java -cp <your-classpath> <fully-qualified-name-of-class> /home/john/myfiles/myprogects/...../input1.txt

To sum up, what you need to know/do is the following:

• the location of your program class and its package (filename)
• the location of your input file (input.txt)
• pass the correct argument accordingly

Answered By - A4L