taylorialcom/ Fundamentals

Command Line

Command Line Arguments

It is possible to run a Java program from the command line like this:

> java taylor.FishingGame

Here the FishingGame class in the taylor package must be the entry point for the program (contains the main() method).

Suppose I wanted to be able to specify the level that the game starts on when I run the program. For example,

> java taylor.FishingGame 3

should start the fishing game on level 3 (it turns out the first two levels are boring).

Java allows us to specify an arbitrary number of command line arguments after the class containing the main() method. These arguments are passed to the main() method as an array of strings. Recall that the main() method looks like this:

public static void main(String[] args) {
    // ...

The args array contains the command line arguments. In this particular example, the array contains one element: {"3"}. Here are some other examples:

Command lineValue of args
java taylor.FishingGame 3 Chris Taylor{"3", "Chris", "Taylor"}
java taylor.FishingGame 3 "Chris Taylor"{"3", "Chris Taylor"}

Command Line Arguments with Jar Files

Specifying command line arguments is very similar when running an executable .jar file:

> java -jar FishingGame.jar 3

Specifying Command Line Arguments in IntelliJ

When running a program in IntelliJ, you can specify the command line argument(s) in the run configuration. To do this,

  1. Load the class with the main() method in the IntelliJ text editor
  2. Right-click in the text area and select Run 'FishingGame.main()' (1 in the figure below)
  3. Click on FishingGame to the right of the Run icon (2 in the figure below)
  4. Select Edit Configurations

Figure [contextMenu]: Run from the Context Menu

  1. Add the desired argument(s) in the Program Arguments box

Figure [programArgs]: Program Arguments

Now, whenever you run this configuration, it will supply the program arguments to the program so that you don't have to retype them each time you run your program.

Command Line Arguments in JavaFX

JavaFX provides additional support for command line arguments. The application class has a getParameters() method that returns an Application.Parameters object. Note: this is an instance method, so you'll need to call it in an instance method, e.g., start(Stage stage).

Take a look at the Application.Parameters class for details on how to access the command line arguments.