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
$

Note: If you are using Java 11 or higher, you don’t need to compile the java source file explicitly. The java command will compile and run the class simultaneously.

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…”.

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.

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.

If you run the class again, the saved run configuration will be used. So if you want to override the command-line arguments or remove them, you will have to open the run configurations window and make necessary changes.

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