Design Patterns Observer Pattern - Design Patterns

What is Design Patterns Observer Pattern?

Observer pattern is use when there is one-to-many relationship between substance such as if one object is modified; its dependent objects are to be notified automatically. Observer pattern falls under behavioural pattern type.


Observer pattern uses three performer classes. Subject, Observer and Client. Topic is an object having methods to connect and detach observers to a customer object. We have created an conceptual class Observer and a concrete class Subject that is extending class Observer.

ObserverPatternDemo, our demonstration class, will use theme and concrete class object to show observer pattern in action.

Step 1

Create Subject class.

Step 2

Create Observer class.

Step 3

Create concrete observer classes

Step 4

Use theme and concrete observer objects.

Step 5

Verify the output.

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