how can i modify main method to get input and output from the comandline?

Question

Instead of hard coding to read the infile and outfile, I want to read from the command line. How would I do that?

/**
 * reads a file and creates a histogram from it
 * @param args string of argument
 * @precondition none
 */
public static void main(String[] args) {
    Histogram hist = new  Histogram();
    FileInputController input = new FileInputController(hist);
    FileOutputController output = new FileOutputController(hist);

    try {
        input.readWords("infile.txt");
        output.writeWords("outfile.txt");
    } catch (FileNotFoundException exception) {
        System.out.println("exception caught! somthing went wrong: " + exception.getMessage());
    } catch (IOException exception) {
        System.out.println("exception caught! somthing went wrong: " + exception.getMessage());
    } finally {
        System.exit(1);
    }
 }

Answer 1

public static void main(String[] args) {
    WordHistogram hist = new  WordHistogram();
    FileInputController input = new FileInputController(hist);
    FileOutputController output = new FileOutputController(hist);

    try {
        input.readWords(args[0]);  //args[0] is the first argument passed while launching Java
        output.writeWords(args[1]);  //args[1] is the second argument passed while launching Java
    } catch (FileNotFoundException exception) {
        System.out.println("exception caught! somthing went wrong: " + exception.getMessage());
    } catch (IOException exception) {
        System.out.println("exception caught! somthing went wrong: " + exception.getMessage());
    } finally {
        System.exit(1);
    }
}

Run your program like: java YourClassName infile.txt outfile.txt

In main(String[] args), args is an array of Strings which contains values of arguments passed while launching Java.

Please DO read Oracle docs about command line arguments for further reading.