Java Reference
In-Depth Information
// Invoke the class method using the class name
MethodType.printM();
System.out.println("Invoking class method on an instance...");
// Invoke the class method using the instance reference
mt.printM();
}
}
Invoking instance method...
printMN() - m = 100
printMN() - n = 200
Invoking class method on class name...
printM() - m = 100
Invoking class method on an instance...
printM() - m = 100
The Special main() Method
You learned about declaring a method in a class in the previous section. Let's discuss the main() method that you
have been using to run your classes. The main() method declaration is as follows:
public static void main(String[] args) {
// Method body goes here
}
Two modifiers, public and static , are used in the declaration of the main() method. The public modifier makes
it accessible from anywhere in the application as long as the class in which it is declared is accessible. The static
modifier makes it a class method, so it can be invoked using a class name. Its return type is void , which means it does
not return a value to its caller. Its name is main and it accepts one parameter of type String array ( String[] ). Note
that you have been using args as the name of its parameter. However, you can use any parameter name you wish. For
example, you can declare the main method as public static void main(String[] myParameters) , which is the
same as declaring the main method as shown above. Whatever parameter name you choose, you will need to use the
same name in the body of the method if you need to refer to the parameter passed to this method.
What is special about the declaration of a main() method in a class? You run a Java application by passing a class
name to the java command. For example, you would use the following command to run the MethodTypeTest class:
java com.jdojo.cls.MethodTypeTest
When the above command is executed, the JVM (the java command essentially starts a JVM) finds and loads
the MethodType class definition in memory. Then, it looks for a method declaration, which is declared as public and
static , returns void , and has a method argument as String array. If it finds the main() method declaration, the
JVM invokes the method. If it does not find the main() method, it does not know where to start the application and it
throws an error stating that no main() method was found.
 
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