One of my kids is taking Java in high school and had this on one of his tests: Which of the following is a valid identifier in Java? a. 123java b. main c. java1234 d. {abce e. )whoot He answered b and got it wrong. I looked at the question and argued that main is … Read more
I’m just beginning to write programs in Java. What does the following Java code mean? public static void main(String[] args) What is String[] args? When would you use these args? Source code and/or examples are preferred over abstract explanations 18 Answers 18
The method signature of a Java mainmethod is: public static void main(String[] args) { … } Is there a reason why this method must be static? 37 s 37
What is the correct (most efficient) way to define the main() function in C and C++ — int main() or void main() — and why? And how about the arguments? If int main() then return 1 or return 0? There are numerous duplicates of this question, including: What are the valid signatures for C’s main() … 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
A common problem that new Java developers experience is that their programs fail to run with the error message: Could not find or load main class … What does this mean, what causes it, and how should you fix it? 5 59
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
In Java args contains the supplied command-line arguments as an array of String objects. In other words, if you run your program as java MyProgram one two then args will contain [“one”, “two”]. If you wanted to output the contents of args, you can just loop through them like this… public class ArgumentExample { public static void main(String[] args) { for(int i = 0; i < args.length; … Read more
What does this do? [python]if __name__ == "__main__": print("Hello world!") [/python] 40 Short 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 … Read more
I have two questions about Exceptions. Firstly, I got this message from my code… Exception in thread “main” java.lang.ArithmeticException: / by zero This error message means dividing by zero, such as by doing int a = 5 / 0; A method can throw an Exception class instance, can’t it? But this is an expression. Why … Read more
