如何从在java中的命令行参数中给出的文件中读取？

Question

I want to read from file , where the program gets the file name ( the file is also a java file) from command line argument , and then prints only the comments from the file i want to read from the file using java.nio.file.Files and java.nio.file.Path maybe. i am supposed to read the file name using the main function i don't know how to do that , any help plz ? this is actually my first ever code i write in java so i am having a lot of difficulties here is what i have so far :

package firtJavaCode;

import java.io.*; 
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.StringTokenizer;
import java.lang.String ;

public class ReadFromFile {

    public static void main(String[] args) {
        try {
            //String filePath = "";   // here is my problem i don't know how to read from a giving file
            String line;
            BufferedReader br = new BufferedReader(new FileReader(filePath));
            int lineNumber = 0;
            while ((line = br.readLine()) != null) {
                lineNumber++;
                if  (line.contains("//")) {
                     StringTokenizer st1 =  new StringTokenizer(line, "//");            
                     System.out.println(st1.nextToken()); 
                }
                
                // i still didn't complete the code , just want to figure how to read from file first
            }
        }catch (Exception e) {
            System.out.println(e);
        }
    }
}

Answer 1

You have the arguments which are written in the console in the String[] args array. To get the filename we assume that you execute the program like this: java example /home/file.txt .

args[0] == "/home/file.txt"

So the filepath is saved in args[0] as a string already so you won't need the extra String filepath in the code.

BufferedReader br = new BufferedReader(new FileReader(args[0]));

So basically the arguments that you put in after the program name are saved all in the String args[] array.

I also would implement a way to check if only the filepath is entered and not some other crap like this:

if (args.length() > 0)
{
    System.out.println("Error! Too many arguments entered!");
}