命令行参数显示0？

Question

package commandLine;

public class commandLine {

public static void main(String[] args) {
    System.out.println("There are " +args.length+ " Command-line Arguments");
    System.out.println("They are: ");
    for(int i=0;i<args.length;i++){
        System.out.println("arg["+i+"]: "+args[i]);
    }

}

}

I wanted to check the length of my command-line arguments and loop through them to display the array of command lines. However, it says my command line arguments are 0? How can this be?

Answer 1

Official Java tutorial about 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. For example, suppose a Java application called Sort sorts lines in a file. To sort the data in a file named friends.txt, a user would enter:

java Sort friends.txt

When an application is launched, the runtime system passes the command-line arguments to the application's main method via an array of Strings. In the previous example, the command-line arguments passed to the Sort application in an array that contains a single String: "friends.txt".

Echoing Command-Line Arguments

The Echo example displays each of its command-line arguments on a line by itself:

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

The following example shows how a user might run Echo. User input is in italics.

java Echo Drink Hot Java

Drink

Hot

Java

Note that the application displays each word — Drink, Hot, and Java — on a line by itself. This is because the space character separates command-line arguments. To have Drink, Hot, and Java interpreted as a single argument, the user would join them by enclosing them within quotation marks.

java Echo "Drink Hot Java" Drink Hot Java

If you are using IDE (Eclipse or etc.) you have to specify command-line arguments via some kind of run configuration. For example for Eclipse :

Answer 2

In have the command line is essentially of the form

java [vm options] class/jar [arguments]

Only these final arguments are given to you in the array. This is unlike a standard C program where you receive the command name also.