Command line arguments in Java are parameters or values that are passed to a Java program at the time of execution through the command line interface. These arguments can be used by the program to modify its behavior or to provide input data. Java programs can access command line arguments through the args parameter of the main method. The args parameter is an array of strings that contains the command line arguments. The first element of the array (args[0]) is the first argument, the second element (args[1]) is the second argument, and so on. For example, consider the following command:

java MyProgram arg1 arg2 arg3

In this command, MyProgram is the name of the Java program, and arg1, arg2, and arg3 are the command line arguments. The main method of the MyProgram class can access these arguments using the args parameter: 

public class MyProgram {
    public static void main(String[] args) {
        System.out.println(args[0]); // prints "arg1"
        System.out.println(args[1]); // prints "arg2"
        System.out.println(args[2]); // prints "arg3"
    }
}

Command line arguments can be used to provide input data to a program, configure its behavior, or specify options. For example, a command line argument could be used to specify a filename, a directory path, a port number, or a debug mode.