What is the primary function of a modifier method?

The primary function of a modifier method is to determine accessibility of fields and methods. Modifier methods, often referred to as accessors (getters) and mutators (setters), are designed to control how the properties of an object can be accessed or modified. By using these methods, a programmer can enforce encapsulation, ensuring that the internal representation of an object is hidden from the outside and altered only in controlled ways.

For example, an object might have private fields which should only be interacted with through public methods. A getter can retrieve the value of a field while ensuring that no external code can directly manipulate it, thus preserving the integrity of the data. Similarly, a setter allows controlled modification of field values, potentially including validation checks to prevent the object from entering an invalid state.

The other options relate to concepts that are not the primary purpose of modifier methods. Creating new instances of classes is typically handled by constructors. Executing database queries is the domain of data access methods, and handling errors in code is usually managed through error handling mechanisms, such as try/catch blocks, rather than modifier methods.