A third difference between Java and Swift is how they implement the observer pattern. The observer pattern defines a one-to-many relationship between an object and several other objects that depend on its state. The object notifies the other objects about any changes in its state, and the other objects update themselves accordingly. This can be useful for creating dynamic and interactive user interfaces, such as buttons, sliders, or text fields. In Java, you can use the observer pattern by defining an observer interface and a subject interface. The observer interface declares a method that is called when the subject changes its state, and the subject interface declares methods for attaching and detaching observers, and for notifying them about the changes. Then, you can create concrete classes that implement the observer and the subject interfaces, and register them with each other. In Swift, you can use the delegation pattern to achieve a similar effect. The delegation pattern is a design pattern that allows an object to delegate some of its responsibilities to another object, without knowing the details of how it performs them. The object that delegates is called the delegator, and the object that performs the tasks is called the delegate. The delegator defines a protocol that specifies the tasks that the delegate can perform, and the delegate conforms to the protocol and implements the tasks. Then, the delegator assigns the delegate as a property, and calls the protocol methods when it needs the delegate's help. For example, instead of using an observer interface and a subject interface, you can use a delegate protocol and a delegator class. The delegate protocol defines a method that is called when the delegator changes its state, and the delegator class defines a delegate property and a method for notifying the delegate. Then, you can create a concrete class that conforms to the delegate protocol and implements the method, and assign it as the delegate of the delegator class.