COMMAND LINE ARGUMENTS

COMMAND LINE ARGUMENTS

•  A Java application can accept any number of arguments from the command line. This allows the user to specify configuration information when the application is launched.
• The user enters command-line arguments when invoking the application and specifies them after the name of the class to be run.
• When an application is launched, the runtime system passes the command-line arguments to the application's main method via an array of Strings.
• Java application can accept any number of arguments directly from the command line. The user can enter command-line arguments when invoking the application. 
• When running the java program from java command, the arguments are provided after the name of the class separated by space.

Example:

• Consider our Java program as sample.java with command line arguments.For that we have give the arguments in command prompt when invoking the program.
• use java sample arg1 arg2 arg3....to run sample java program.

Program: 

public class Sample {
    public static void main (String[] args) {
        for (String s: args) {
            System.out.println(s);
        }
    }
}

Compilation:

use the following code to run this program

javac Sample.java

java Sample Hai Hello World

Output:

Hai

Hello

World

Note: 

• If you want give single command line argument for the same Output(above output), 

• Compile the program and run using the code

  java Sample "Hai Hello World"

Output:

Hai Hello World

Parsing Numeric Command-Line Arguments

• If your program needs to support a numeric command-line argument, it must convert a String argument that represents a number, such as "8", to a numeric value. 

Example:

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

int firstArg;
if (args.length > 0) {
    try {
        firstArg = Integer.parseInt(args[0]);
    } catch (NumberFormatException e) {
        System.err.println("Argument"
            + " must be an integer");
        System.exit(1);
    }
}

}

} 

• parseInt throws a NumberFormatException if the format of args[0] isn't valid. All of the Number classes — Integer, Float, Double, and so on — have parseXXX methods that convert a String representing a number to an object of their type