TOTO

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 );
        }
}

有这个习惯的，一般是从C语言过来的人，因为在C语言里面没有这么麻烦的东西，直接调用就行了，
但是Java是面向对象的。
类的静态成员函数是属于类的，不是对象的，也就是说即使对象不存在，它照样可以用，由于它不属于对象，
那么它就无法调用对象里面的静态函数。
关于static在C++的用法，大家可以参考下面这篇文章：
http://dev.csdn.net/article/19/article/20/20219.shtm