Java Language - 11 - Command-Line Arguments

Java Fundamentals – Command-Line Arguments

Introduction

Command-line arguments are a way to pass information to a Java program when it is launched from the command line. These arguments provide a means for making a Java application more flexible and customizable, allowing users to influence its behavior by providing input at runtime. In this guide, we’ll explore the use of command-line arguments in Java.

Passing Command-Line Arguments

To pass command-line arguments to a Java program, you include them after the `java` command and the program’s main class. They are separated by spaces. For example:


java MyProgram arg1 arg2 arg3

In this example, `MyProgram` is the name of the Java class, and `arg1`, `arg2`, and `arg3` are the command-line arguments.

Accessing Command-Line Arguments in Java

Java provides access to command-line arguments through the `args` parameter in the `main` method. The `main` method is the entry point of a Java program, and it is defined as follows:


public static void main(String[] args) {
    // Your program logic here
}

The `args` parameter is an array of strings where each element represents a command-line argument passed to the program.

Using Command-Line Arguments in Your Program

Once you have access to the command-line arguments, you can use them in your program. Here’s an example of a simple Java program that calculates the sum of two numbers provided as command-line arguments:


public class CommandLineSum {
    public static void main(String[] args) {
        if (args.length < 2) {
            System.out.println("Please provide two numbers as command-line arguments.");
        } else {
            try {
                double num1 = Double.parseDouble(args[0]);
                double num2 = Double.parseDouble(args[1]);
                double sum = num1 + num2;
                System.out.println("Sum: " + sum);
            } catch (NumberFormatException e) {
                System.out.println("Invalid input. Please provide valid numbers.");
            }
        }
    }
}

In this program, we check if there are at least two command-line arguments. If so, we attempt to parse them as numbers, calculate their sum, and display the result. If the input is not valid, we handle the exception and provide an error message.

Common Use Cases for Command-Line Arguments

Command-line arguments are versatile and can be used for various purposes in Java applications. Some common use cases include:

Configuration: You can use command-line arguments to provide configuration options to your program, such as file paths, database connection details, or user settings.
Batch Processing: For batch processing tasks, you can specify input and output files or directories as command-line arguments.
Customization: Users can customize the behavior of your application by passing arguments. For example, you might offer different modes or features based on user input.

Best Practices

When working with command-line arguments, it’s essential to follow best practices to ensure your program is user-friendly and robust:

Check Argument Count: Verify that the correct number of arguments is provided to avoid unexpected errors.
Validate Input: Ensure that the input provided as arguments is of the expected format and type to prevent exceptions and errors.
Provide Help: Consider implementing a help option to display information about how to use the program, especially when it has multiple arguments or options.

Conclusion

Command-line arguments are a powerful way to make your Java applications more versatile and adaptable to different use cases. By understanding how to pass and process command-line arguments, you can create applications that provide users with greater control and customization.

Java Language – 11 – Command-Line Arguments