Short Answer It’s boilerplate code that protects users from accidentally invoking the script when they didn’t intend to. Here are some common problems when the guard is omitted from a script: If you import the guardless script in another script (e.g. import my_script_without_a_name_eq_main_guard), then the second script will trigger the first to run at import … Read more
I have installed an application, when I try to run it (it’s an executable jar) nothing happens. When I run it from the commandline with: java -jar “app.jar” I get the following message: no main manifest attribute, in “app.jar” Normally, if I had created the program myself, I would have added a main class attribute … Read more
First, it’s kind of weird, to see you run java -jar “app” and not java -jar app.jar Second, to make a jar executable… you need to jar a file called META-INF/MANIFEST.MF the file itself should have (at least) this one liner: Where com.mypackage.MyClass is the class holding the public static void main(String[] args) entry point. Note that there are several ways to … Read more
The java <class-name> command syntax First of all, you need to understand the correct way to launch a program using the java (or javaw) command. The normal syntax1 is this: where <option> is a command line option (starting with a “-” character), <class-name> is a fully qualified Java class name, and <arg> is an arbitrary command line argument that gets passed to your application. 1 – There … Read more
The java <class-name> command syntax First of all, you need to understand the correct way to launch a program using the java (or javaw) command. The normal syntax1 is this: where <option> is a command line option (starting with a “-” character), <class-name> is a fully qualified Java class name, and <arg> is an arbitrary … Read more
Short Answer It’s boilerplate code that protects users from accidentally invoking the script when they didn’t intend to. Here are some common problems when the guard is omitted from a script: If you import the guardless script in another script (e.g. import my_script_without_a_name_eq_main_guard), then the second script will trigger the first to run at import … Read more