Why command line arguments are used in Java

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Introduction

Command line arguments let users give information to a program when they start it. This helps the program work differently without changing its code.

When you want to let users choose a file to open without changing the program.

When you want to set options like 'verbose mode' or 'debug mode' before running the program.

When you want to pass numbers or words to the program to process, like a calculator program.

When you want to run the same program with different inputs quickly from the command line.

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Syntax

Java

public static void main(String[] args) {
    // args is an array of strings holding command line arguments
}

args holds all the words typed after the program name in the command line.

Each word is a separate string in the args array.

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Examples

line_end_arrow_notchThis prints the first word typed after the program name.

Java

public static void main(String[] args) {
    System.out.println("First argument: " + args[0]);
}

line_end_arrow_notchThis prints all the command line arguments one by one.

Java

public static void main(String[] args) {
    for (String arg : args) {
        System.out.println(arg);
    }
}

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Sample Program

This program checks if any command line arguments were given. If yes, it prints how many and what they are.

Java

public class CommandLineExample {
    public static void main(String[] args) {
        if (args.length == 0) {
            System.out.println("No arguments provided.");
        } else {
            System.out.println("You provided " + args.length + " arguments:");
            for (int i = 0; i < args.length; i++) {
                System.out.println("Argument " + (i + 1) + ": " + args[i]);
            }
        }
    }
}

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Important Notes

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If you run the program without any arguments, args.length will be zero.

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Arguments are always strings. You need to convert them if you want numbers.

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Summary

Command line arguments let users give input to programs when starting them.

They help programs behave differently without changing code.

Arguments are accessed as strings in the args array in main.