Java Command Line Arguments - String[] args Explained

⏱️ 7 min read • Beginner Level • Lesson 20

Command line arguments in Java are values passed to a program at the time of execution. These values are received inside the main() method using the String[] args array.

Before learning command line arguments, you should understand Java Input Output, Java Program Structure, and Java Arrays.

What are Command Line Arguments in Java?

Command line arguments are values given after the class name when running a Java program from terminal or command prompt.

java ClassName argument1 argument2 argument3

String[] args in main Method

In Java, the main() method contains a one-dimensional array of String type. This array receives command line arguments.

public static void main(String[] args) {
    // args stores command line arguments
}

Example: Single Command Line Argument

In this example, we receive one command line argument and print it.

public class CommandLineDemo {
    public static void main(String[] args) {
        String firstArgument = args[0];
        System.out.println("Argument is: " + firstArgument);
    }
}

Compile and Run:

javac CommandLineDemo.java
java CommandLineDemo JavaProwess

Output:

Argument is: JavaProwess

Example: Multiple Command Line Arguments

You can pass any number of command line arguments. Arguments are separated by spaces. Java stores them in the args array.

public class MultipleArgumentsDemo {
    public static void main(String[] args) {
        for (int i = 0; i < args.length; i++) {
            System.out.print(args[i] + " ");
        }
    }
}

Compile and Run:

javac MultipleArgumentsDemo.java
java MultipleArgumentsDemo C C++ and "Java Prowess"

Output:

C C++ and Java Prowess

Passing Arguments with Spaces

By default, spaces separate command line arguments. If you want to pass a value containing spaces, use double quotes.

public class ArgumentWithSpaces {
    public static void main(String[] args) {
        System.out.println(args[0]);
    }
}

Run:

java ArgumentWithSpaces "Java Programming"

Output:

Java Programming

Using Numeric Command Line Arguments

Command line arguments are received as strings. To use them as numbers, you must convert them using methods like Integer.parseInt().

public class AddNumbers {
    public static void main(String[] args) {
        int number1 = Integer.parseInt(args[0]);
        int number2 = Integer.parseInt(args[1]);

        int sum = number1 + number2;

        System.out.println("Sum: " + sum);
    }
}

Compile and Run:

javac AddNumbers.java
java AddNumbers 10 20

Output:

Sum: 30

Checking Number of Arguments

It is a good practice to check args.length before accessing command line arguments. This helps avoid errors when the user forgets to pass arguments.

public class ArgumentCheck {
    public static void main(String[] args) {
        if (args.length == 0) {
            System.out.println("Please pass at least one argument.");
            return;
        }

        System.out.println("First Argument: " + args[0]);
    }
}

Run without argument:

java ArgumentCheck

Output:

Please pass at least one argument.

Scanner Input vs Command Line Arguments

Common Mistakes with Command Line Arguments

Command Line Arguments at a Glance

Frequently Asked Questions

🧠 Test your understanding with a quick quiz

public class Add {
    public static void main(String[] args) {
        int a = Integer.parseInt(args[0]);
        int b = Integer.parseInt(args[1]);
        System.out.println(a + b);
    }
}

public class Demo {
    public static void main(String[] args) {
        System.out.println(args[0]);
    }
}

🎉 Great job! Continue learning Java step by step.