Java - Accessing non-static member variables from static methods (such as main)

Many programmers, particularly when first introduced to Java, have problems with accessing member variables from their main method. The method signature for main is marked static - meaning that we don't need to create an instance of the class to invoke the main method. For example, a Java Virtual Machine (JVM) could call the class MyApplication like this :-

MyApplication.main ( command_line_args );

This means, however, that there isn't an instance of MyApplication - it doesn't have any member variables to access! Take for example the following application, which will generate a compiler error message.

public class StaticDemo
{
       public String my_member_variable = "somedata";

        public static void main (String args[])
       {
  // Access a non-static member from static method
               System.out.println ("This generates a compiler error" +
   my_member_variable );
       }
}

If you want to access its member variables from a non-static method (like main), you must create an instance of the object. Here's a simple example of how to correctly write code to access non-static member variables, by first creating an instance of the object.

public class NonStaticDemo
{
       public String my_member_variable = "somedata";

       public static void main (String args[])
       {
               NonStaticDemo demo = new NonStaticDemo();

  // Access member variable of demo
               System.out.println ("This WON'T generate an error" +
                       demo.my_member_variable );
       }
}