Declares the name of a module and introduces the definition of the variables, properties, events, and procedures that the module comprises.
A Module statement defines a reference type available throughout its namespace. A module (sometimes called a standard module)is similar to a class but with some important distinctions. Every module has exactly one instance and does not need to be created or assigned to a variable. Modules do not support inheritance or implement interfaces. Notice that a module is not a type in the sense that a class or structure is — you cannot declare a programming element to have the data type of a module.
You can use Module only at namespace level. This means the declaration context for a module must be a source file or namespace, and cannot be a class, structure, module, interface, procedure, or block. You cannot nest a module within another module, or within any type. For more information, see Declaration Contexts and Default Access Levels (Visual Basic).
A module has the same lifetime as your program. Because its members are all Shared, they also have lifetimes equal to that of the program.
All members of a module are implicitly Shared.
Classes and Modules
These elements have many similarities, but there are some important differences as well.
Terminology. Previous versions of Visual Basic recognize two types of modules: class modules (.cls files) and standard modules (.bas files). The current version calls these classes and modules, respectively.
Shared Members. You can control whether a member of a class is a shared or instance member.
Object Orientation. Classes are object-oriented, but modules are not. So only classes can be instantiated as objects. For more information, see Objects and Classes in Visual Basic.
Modifiers. All module members are implicitly Shared (Visual Basic). You cannot use the Shared keyword when declaring a member, and you cannot alter the shared status of any member.
Inheritance. A module cannot inherit from any type other than Object, from which all modules inherit. In particular, one module cannot inherit from another.
Default Property. You cannot define any default properties in a module. For more information, see Default (Visual Basic).
Access Level. Within a module, you can declare each member with its own access level. Module members default to Public (Visual Basic) access, except variables and constants, which default to Private (Visual Basic) access. When a module has more restricted access than one of its members, the specified module access level takes precedence.
Scope. A module is in scope throughout its namespace.
The scope of every module member is the entire module. Notice that all members undergo type promotion, which causes their scope to be promoted to the namespace containing the module. For more information, see Type Promotion (Visual Basic).
Qualification. You can have multiple modules in a project, and you can declare members with the same name in two or more modules. However, you must qualify any reference to such a member with the appropriate module name if the reference is from outside that module. For more information, see References to Declared Elements (Visual Basic).