# observer pattern

CEFR C1 · Compound

Source: https://englishreference.com/word/observer-pattern
Updated: 2026-07-22

## Definition

a way of designing software where one object keeps a list of other objects and tells them automatically when its state changes. You use this so that different parts of a program stay updated without being tightly connected to each other.

For teachers: a software design pattern in which an object, called the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes. This pattern facilitates loose coupling by allowing the subject to interact with observers through a generic interface rather than specific implementations.

## Examples

- The app uses the observer pattern to update the screen when data changes.
- By implementing the observer pattern, the developers ensured that the user interface and the database remained synchronized without direct dependencies.
- The observer pattern is fundamental to event-driven architectures, enabling a one-to-many dependency relationship where multiple subscriber objects can react dynamically to events published by a single provider.

## Usage notes

- Commonly used in the context of object-oriented programming and software architecture.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.