Command Line Arguments in Java

Command-line arguments in Java are values passed to a program during execution through the command prompt. These arguments are stored as String values in the main() method parameter.

• Used to provide input without hardcoding values in the program.
• Helps make programs flexible and reusable for different inputs.
• Commonly used for file names, configuration values, and user data at runtime.

Command-line arguments are passed after the class name while running the Java program.

Syntax:

java Geeks Hello World

• The JVM collects these values and passes them to the main(String[] args) method.
• Hello -> stored in args[0]
• World -> stored in args[1]

Example: In this example, we are going to print a simple argument in the command line.

class GFG{

    public static void main(String[] args) {
      
        // Printing the first argument
        System.out.println(args[0]);
    }
}

Output:

Explanation:

• Running java GFG GeeksForGeeks prints GeeksForGeeks because the argument is passed to main(String[] args).
• If no arguments are given (e.g., java GFG), it throws ArrayIndexOutOfBoundsException since args is empty.

Working of Command-Line Arguments

• Command-line arguments in Java are space-separated values passed to the main(String[] args) method.
• JVM wraps them into the args[] array, where each value is stored as a string (e.g., args[0], args[1], etc.).
• The number of arguments can be checked using args.length.

Example: Display Command-Line Arguments Passed to a Java Program

To compile and run a Java program in the command prompt, follow the steps written below.

• Save the program as Hello.java
• Open the command prompt window and compile the program- javac Hello.java
• After a successful compilation of the program, run the following command by writing the arguments- java Hello
• For example - java Hello Geeks at GeeksforGeeks
• Press Enter and you will get the desired output.

class Hello {

    // Main driver method
    public static void main(String[] args)
    {
        // Checking if length of args array is
        // greater than 0
        if (args.length > 0) {

            // Print statements
            System.out.println("The command line"
                               + " arguments are:");

            // Iterating the args array
            // using for each loop
            for (String val : args)

                System.out.println(val);
        }
        else

            System.out.println("No command line "
                               + "arguments found.");
    }
}

Output: