Method (computer Science) - Accessor and Mutator Methods

Accessor and Mutator Methods

An 'accessor' method is a method that is usually small, simple and provides the sole means for the state of an object to be accessed (retrieved) from other parts of a program.

Although this introduces a new dependency, as stated above, use of methods is preferred, in the object-oriented paradigm, to directly accessing state data - because those methods provide an abstraction layer. For example, if a bank-account class provides a getBalance accessor method to retrieve the current balance (rather than directly accessing the balance data fields), then later revisions of the same code can implement a more complex mechanism for balance retrieval (say, a database fetch), without the dependent code needing to be changed (However, this often claimed advantage is not unique to object oriented programming, and was earlier implemented - when desirable in critical systems - through conventional modular programming with optional run-time, system-wide locking mechanisms, in the imperative/procedural paradigms).

To compare the value of two data items, two accessor-method calls are normally required before a comparison can take place between the retrieved primitive data type values. Comparator methods are required to compare entire objects for equality. This contrasts with a direct comparison in non-OOP paradigms. An update, modifier, or mutator method, is an accessor method that changes the state of an object. Objects that provide such methods are considered mutable objects.