Java Command-Line Arguments

The command-line arguments in Java allow us to pass arguments during the execution of the program.

As the name suggests arguments are passed through the command line.

Example: Command-Line Arguments

class Main {
  public static void main(String[] args) {
    System.out.println("Command-Line arguments are");

    // loop through all arguments
    for(String str: args) {
      System.out.println(str);
    }
  }
}

Let's try to run this program using the command line.

1. To compile the code

javac Main.java

2. To run the code

java Main

Now suppose we want to pass some arguments while running the program, we can pass the arguments after the class name. For example,

java Main apple ball cat

Here apple, ball, and cat are arguments passed to the program through the command line. Now, we will get the following output.

Command-Line arguments are
Apple
Ball
Cat

In the above program, the main() method includes an array of strings named args as its parameter.

public static void main(String[] args) {...}

The String array stores all the arguments passed through the command line.

Note: Arguments are always stored as strings and always separated by white-space.

Passing Numeric Command-Line Arguments

The main() method of every Java program only accepts string arguments. Hence it is not possible to pass numeric arguments through the command line.

However, we can later convert string arguments into numeric values.

Example: Numeric Command-Line Arguments

class Main {
  public static void main(String[] args) {

    for(String str: args) {
      // convert into integer type
    int argument = Integer.parseInt(str);
    System.out.println("Argument in integer form: " + argument);
    }

  }
}

Let's try to run the program through the command line.

// compile the code
javac Main.java

// run the code
java Main 11 23

Here 11 and 23 are command-line arguments. Now, we will get the following output.

Arguments in integer form
11
23

In the above example, notice the line

int argument = Intege.parseInt(str);

Here, the parseInt() method of the Integer class converts the string argument into an integer.

Similarly, we can use the parseDouble() and parseFloat() method to convert the string into double and float respectively.

Note: If the arguments cannot be converted into the specified numeric value then an exception named NumberFormatException occurs.