Java：使用Scanner类无需管道即可从文件读取输入

Question

I currently have an implementation of a program where I read in the input using the Scanner class. Integer by integer. I do this by piping the input file via the command line.

java program < input.txt

I need to avoid piping the input by using an argument on the command line to open the file in my program.

java program --file=input.txt

or something similar. I understand that I could parse the command line argument, extract the text "input.txt" and then use a class like "BufferedReader" or something similar to read the file.

I am just curious if there is away to use the input file (no piping) AND still use the Scanner class. Which means I wouldn't have to change over my nextInt() and other such calls.

Answer 1

Since arguments are just not evaulated but passed to your main(String[] args) method without any work in the middle your only option is to parse the argument, extract the filename input.txt and open it as a normal file stream.

I wouldn't see how it should infer that a file must be opened and passed as a pipe without being a pipe.. you can easily use Scanner with a File argument without bothering about anything..

public Scanner(File source) throws FileNotFoundException

Constructs a new Scanner that produces values scanned from the specified file. Bytes from the file are converted into characters using the underlying platform's default charset.