Command Line Arguments in Java

Command-line arguments in Java are used to pass arguments to the main program. If you look at the Java main method syntax, it accepts String array as an argument.

When we pass command-line arguments, they are treated as strings and passed to the main function in the string array argument. The arguments have to be passed as space-separated values.

We can pass strings and primitive data types as command-line arguments. The arguments will be converted to strings and passed into the main method string array argument.

Command Line Arguments in Java

Let’s say we have a simple java class to print command line arguments values.

package com.journaldev.examples;

public class CommandLineArguments {

	public static void main(String[] args) {
		System.out.println("Number of Command Line Argument = "+args.length);
		
		for(int i = 0; i< args.length; i++) {
			System.out.println(String.format("Command Line Argument %d is %s", i, args[i]));
		}
	}

}

If we run this class without any arguments, the output will be as follows.

$ java com/journaldev/examples/CommandLineArguments.java
Number of Command Line Argument = 0

Now, let's pass some arguments to the main class. We have to pass the arguments as space-separated values.

$ java com/journaldev/examples/CommandLineArguments.java "A" "B" "C"
Number of Command Line Argument = 3
Command Line Argument 0 is A
Command Line Argument 1 is B
Command Line Argument 2 is C
$ java com/journaldev/examples/CommandLineArguments.java 1 2 3      
Number of Command Line Argument = 3
Command Line Argument 0 is 1
Command Line Argument 1 is 2
Command Line Argument 2 is 3
$

How to Pass Command Line Arguments in Eclipse

We can also pass command-line arguments to a program in Eclipse using Run Configurations.

Step 1: Open the Class Run Configurations Settings

From the class editor, right click and chose "Run As" -> "Run Configurations...".

Eclipse Run Configurations

Step 2: Specify the Program Arguments in the Arguments Tab

In the pop up window, click on the Arguments tab. Then provide the command line arguments value in the "Program Arguments" text box.

Eclipse Command Line Arguments

Step 3: Click on the Run button

When you will click on the Run button, the run configurations will be saved and the program will execute with the specified command-line arguments.

Eclipse Command Line Arguments Example

Conclusion

The command-line arguments are used to provide values that are essential to run the program. For example, we can specify the database credentials to be used by the program. We can specify the configuration file location from where the program should pick the required values.

Reference: Command-Line Arguments Oracle Docs