Command Line Arguments in Java

Java command-line argument is an argument, i.e., passed at the time of running the Java program. Command-line arguments passed from the console can be received by the Java program and used as input.

Example:

java Geeks Hello World

Note: Here, the words Hello and World are the command-line arguments. JVM will collect these words and will pass these arguments to the main method as an array of strings called args. The JVM passes these arguments to the program inside args[0] and args[1].

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

// Java Program to Illustrate First Argument 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.

Why Use Command Line Arguments?

• It is used because it allows us to provide input at runtime without modifying the whole program.
• It helps to run programs automatically by giving them the needed information from outside.

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 Geeks {  // 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: