How can you check if a string in ABAP is empty?

In ABAP, checking if a string is empty can be done using the construct "IS NOT INITIAL." This method evaluates whether the variable has been assigned any value at all. If a string variable has not been assigned any value, it is considered "initial," meaning it is empty. Therefore, using "IS NOT INITIAL" allows you to confirm that the string actually contains data.

The other options serve different purposes: "IS EMPTY" explicitly checks if a string is empty, but it is not a standard ABAP syntax. "IS BOUND" checks whether an object reference is bound to an instance of a class, not relevant for string checking. "IS SUPPLIED" determines if a formal parameter has been passed to a method or function, which is also not applicable to simply checking if a string is filled. Thus, "IS NOT INITIAL" effectively conveys the emptiness check for strings in ABAP, making it the correct choice.