Release 10.1A: OpenEdge Getting Started:
Object-oriented Programming

> ## Comparing class files and procedure files

> A class file has many similarities to a procedure file but there are some differences. Both class files and procedure files define a main block in which state and behavior are defined. Unlike procedure files, which are more free form, the main block of a class file must be defined between a starting `CLASS` statement and a terminating `END` `CLASS` statement. The `CLASS` statement is necessary to specify the class type and other information required to support the class definition, such as any inheritance or interface specifications.

> As with procedure files that allow data elements scoped to the procedure file to be defined outside of any internal procedure or user-defined function definitions, data members scoped to a class are specified with `DEFINE` statements in its main block, outside of any method definitions. Unlike procedure files, no executable code can appear in the main block that is outside of method definitions and `ON` statements. In addition, a class file cannot define parameters for its main block. Classes support an optional constructor to take any parameters and execute any code when the class is instantiated.

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