Design Fall 2019 3. (15 points) The observer design pattern. The observer pattern attaches a munber of observer objects to a core object. These observer objects get updated whenever a change has occurred within the core object and respond to that change individually and independently. This pattern adheres to the Separation of Concerns principle for software design. in that each observer object performs its own task without having to concera itself with other obeerver objects. In the following questions, you mnst define three classes to make the following testing code work. Hint: Refer to the last page of the ezora for en ermele implementetion for the observer pattert. core Artiele ('A Study of the Test-Drives Develegment Proces) catablssh consectione between the cere and ste ebeervers le.observer LetterCoustObeerver (core) core.attach (le.ebserver) we.observer = WordCoustObaerver (core) core.attach (we.ebserver) # core 'aobservers will be netslied with the change in property tile core. tisl eTest-Driven Development' (a) (6 points) Define a core class Article, which contains a single property (not attribute) called titie. The core class must be able to attach any mumber of observer objects, and must be able to notity the observers once its property title is updated. Saoiteia (b) (3 points) Define an observer class LetterCountObserver, which counts and prints the umber of letters (including white spaces) in the property title, after noticing any change occurred to title in the core object. Design Fall 2019 3. (15 points) The observer design pattern. The observer pattern attaches a munber of observer objects to a core object. These observer objects get updated whenever a change has occurred within the core object and respond to that change individually and independently. This pattern adheres to the Separation of Concerns principle for software design. in that each observer object performs its own task without having to concera itself with other obeerver objects. In the following questions, you mnst define three classes to make the following testing code work. Hint: Refer to the last page of the ezora for en ermele implementetion for the observer pattert. core Artiele ('A Study of the Test-Drives Develegment Proces) catablssh consectione between the cere and ste ebeervers le.observer LetterCoustObeerver (core) core.attach (le.ebserver) we.observer = WordCoustObaerver (core) core.attach (we.ebserver) # core 'aobservers will be netslied with the change in property tile core. tisl eTest-Driven Development' (a) (6 points) Define a core class Article, which contains a single property (not attribute) called titie. The core class must be able to attach any mumber of observer objects, and must be able to notity the observers once its property title is updated. Saoiteia (b) (3 points) Define an observer class LetterCountObserver, which counts and prints the umber of letters (including white spaces) in the property title, after noticing any change occurred to title in the core object