CSIS 110 - Lecture 30
Reading: Appendix E (pages 432-434)
Quiz Wednesday. Covers material up through last lecture.
Main
So far, we have only executed our java classes inside of BlueJ. What if we wanted to
share a program with someone else?
Let's run my tic-tac-toe program.
In order to do this, one of the classes in our program must contain a method with this
signature:
public static void main( String[] args )
Let's look at the parts:
- public – it's a public method, which means it can be invoked from other methods
- void – it doesn't have a return value
- String[] args – it has a formal parameter: an array of Strings
But what does static mean?
It means that this method can be called without having an instance of the class. We've
used class methods without realizing it: Math.sqrt() – I didn't create a Math object and
then call the square root method on that object. Instead, I just called the method using the
form <class name>.<method name>
Static methods are also called class methods.
main is a special static method – when we start java, it looks for a method named main
and calls it – that is what makes our program execute.
What does this mean – it means we can develop a program in java and send the class files
to someone else. That person doesn't need BlueJ or the java development kit (JDK) to run
the program (although they must have the java runtime environment (JRE) installed).
Run from a command window: java TicTacToeGame (note that .class is not part
of the command) – TicTacToeGame is the name of the class that contains the main
method.
Let's add a main method to the AddressBook project (in chapter 5):
- Create a main method in class Address book, create an Address object, and
invoke its start method
