我应该在哪里使用命令行参数而不是Scanner？

Question

I know that when you create your main method of a Class in Java you create it as follows:

public static void main(String[] args)

I also know that the array of Strings named args it's used to enter command-line parameters in the main method but I develop my applications on Eclipse and I never had used it because I always have entered my values by Scanner .

It is a bad practise to use Scanner instead of command-line parameters? Has args array another purpose? When should I use args array?

Thanks in advance!

Answer 1

In reverse order:

When should I use args array?

When you are passing command-line parameters.

Has args array another purpose?

No. It's for passing command-line parameters.

Is it a bad practise to use Scanner instead of command-line parameters?

It's not always possible to use a Scanner . A Scanner might read from STDIN, but in many UNIX systems it is prefered to read command input from STDIN and use command line arguments for program options (eg --help or -h ).

Answer 2

Scanner and the parameter for main are two completely different things. A scanner can be used to ask the user for some kind of action. The parameters for main are relevant when you want to launch the jar either from another application or via commandline. Cooked down: whether to use Scanner or parameters is rather a question of the design of the software, not coding-style.

Answer 3

It entirely depends on your circumstances. Ask yourself the question: "Where are the values coming from? What is the best way for my program to receive these values?"

If the answer is "a user", then prompting the user, thereby guiding the user to the values needed, is likely the best answer.

Any other answer means the values are likely coming from some automated process, which means that "prompting" is a bad choice. Now there are suddenly a lot of choices, again controlled by your circumstances:

• Command-line arguments
• Configuration file
• Data file (eg CSV file)
• Network communication (eg web service)
• Database
• ... and many more

Sometimes a combination is appropriate, eg a command-line argument to find the configuration file , which may include a directory to scan for data files .

You can even do both "prompting" and command-line arguments. If all needed values are supplied as arguments, use them, otherwise prompt for the missing values. Providing no arguments would then prompt for all values.