NullObjekt

NullObjekt, often written Null-Objekt in German, refers to the Null Object design pattern in software engineering. The pattern provides an object that conforms to a given interface but implements neutral, no-op behavior. Instead of returning null, a component supplies a harmless object that can be used through the same code paths without null checks.

The core idea is to avoid null reference errors and scattered null tests by substituting a nonfunctional instance that maintains the contract of the interface. This can simplify client code and improve readability while preserving polymorphism.

Origin and usage: The pattern is described in Martin Fowler’s Patterns of Enterprise Application Architecture and is widely used in object-oriented languages such as Java, C++, and Python. It is popular in systems with plugins, event listeners, or service interfaces where a missing component must be represented safely.

Implementation: Implement a concrete class that implements the interface and whose methods do nothing or return default values. For example, a Logger interface may have a NullLogger that implements log methods by performing no action. Code that obtains a logger can use the instance without null checks.

Benefits and drawbacks: Benefits include fewer null checks, safer default behavior, and simpler APIs. Drawbacks include extra classes and the possibility of masking real problems or incurring small performance costs. The pattern is commonly used with dependency injection or along with language features for optional values.