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In contrast to many other modern programming languages, ABAP is not case-sensitive for ABAP words (tokens of an ABAP statement that express its semantics; either ABAP keywords or additions) nor for operators and names of operands. The only exception is dynamic programming, where the names of operands usually have to be specified in uppercase.
Do not mixed uppercase and lowercase in names
Use only lowercase or uppercase in an individual token. Use uppercase for keywords and lowercase for operands.
The usage of uppercase or lowercase for tokens, that is ABAP words and names, used to be a very important aspect for the formatting of the source code. Uniform case-sensitivity made it easier for the reader to distinguish keywords from names. Due to the source code coloring in the syntax in ABAP Editor, this aspect has become less important; however, the above rule is still valid because of the following reasons:
Because of the second point, it does not make sense in ABAP to use uppercase and lowercase as a self-defined means of style. In other words, the names should not be written in mixed case style (also referred to as camel case style; see the following example), as is very popular in languages that are case-sensitive. A consistent notation cannot be ensured due to the missing relevance in the syntax. A mixed notation will be lost sooner or later when Pretty Printer is used, even if this is unintentional. Moreover, it possibly prevents other developers from using Pretty Printer after changes have been made to the source code. Use of Pretty Printer is explicitly recommended.
When the program PGL_UPPER_LOWER_CASE is executed, source code is displayed in ABAP Editor; the upper part shows the declaration of a class with names in mixed case style or camel case style. Here, uppercase marks the beginnings of words within a combined name.
The code provided here as a bad example approximately follows the Java convention, and in the eyes of many beholders it might look better than the following good example. However, its appearance is less important than the technical restrictions mentioned, which do not currently allow naming like this. Executing Pretty Printer would irreversibly spoil the code's appearance because the names would then be illegible.
The lower part of the source code shows the declaration of a class in ABAP style, where which words within combined names are separated by underscores (_). These separations cannot get lost when Pretty Printer is used.
Once the program has been called, the example is formatted according to the proposed Pretty Printer setting, with ABAP words in uppercase and operands in lowercase. Regardless of its configuration, the separation of the words in the names would be preserved after each execution of Pretty Printer.
The built-in character string functions, to_mixed and from_mixed allow conversions between names in ABAP style with underscores and names in mixed case style or camel case style, which can be helpful for data exchange with external systems.