Observer vs visitor pattern

The object which is being watched is called the subject. The objects which are watching the state changes are called observers or listeners .

An Observable is simply an object where you can observe it’s actions. So anything where you can listen to an action and then be told that action occurs is an Observable . This means an Event Listener is one .

Event Driven Architecture (is a message-driven architecture), responsible to deliver message to Subscriber, asynchronously. Observer Pattern (is a software design pattern), responsible to command Subscriber to do something, synchronously.