Design PatternsReview. CSE 110 Discussion - Week10

Transcription

1 Design PatternsReview CSE 110 Discussion - Week10

2 Question 1 (Take 5 mins.) We have a weather data object which contains information about current temperature, humidity and pressure of the environment. We have a display that wants to display this information. Note that the display would be updated whenever there is a change in one of these measurements. What design pattern you would use to propagate this information and why. Things to consider What if there are multiple displays? How would those get updated in real time without polling weather data class to know about any changes?

3 Question 1 (Cont.)

4 Answer 1: Observer Pattern

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7 Question 2(Take 5 mins.) You have a window interface object with a draw and get description method. But, now you realize that you want some more dynamic behaviors for this window, that is you want to build a window with a horizontal scrollbar and a vertical scrollbar. What design principle would you use and how? Here s your window interface Public interface Window { public void draw(); Draws the window public String getdescription(); // Returns a description of the window

8 Question 2(Cont.) Here s some sample code Public interface Window { public void draw(); Draws the window public String getdescription(); // Returns a description of the window class SimpleWindow implements Window { public void draw() { // Draw window public String getdescription() { return "simple window";

9 Answer 2: Decorator Pattern

10 // abstract decorator class - note that it implements Window abstract class WindowDecorator implements Window { protected Window windowtobedecorated; // the Window being decorated public WindowDecorator (Window windowtobedecorated) { this.windowtobedecorated = windowtobedecorated; public void draw() { windowtobedecorated.draw(); //Delegation public String getdescription() { return windowtobedecorated.getdescription(); //Delegation

11 // The second concrete decorator which adds horizontal scrollbar functionality class HorizontalScrollBarDecorator extends WindowDecorator { public HorizontalScrollBarDecorator (Window windowtobedecorated) { public void draw() { super.draw(); drawhorizontalscrollbar(); private void drawhorizontalscrollbar() { // Draw the horizontal public String getdescription() { return super.getdescription() + ", including horizontal scrollbars";

12 Question 3 (Take 5 minutes) We have a shopping cart class which contains a bunch of items. Now, you want to pay for these items. You can pay using credit card, paypal, google wallet etc. What design principle you would use to handle the payments through these various payment methodologies and how?

13 Here s how your shopping cart looks like - public class ShoppingCart { List<Item> items=new ArrayList<Item>(); public void additem(item item){ this.items.add(item); public int calculatetotal(){ int sum = 0; for(item item : items){ sum += item.getprice(); return sum; // You have to add a pay method here.

14 Answer 3: Strategy Pattern

15 Question 4 (Take 5 minutes) We have an Audio Player that is capable of playing only mp3 files. Now we want this audio player to extend itself to use another Advanced Audio Player that is capable of playing vlc and mp4 files. What design pattern would you use to implement this scenario? Can you draw a UML diagram to depict the implementation?

16 Answer 4: Adapter Pattern We would create an adapter class MediaAdapter which would implement the MediaPlayerinterface and use AdvancedMediaPlayer objects to play the required format. AudioPlayer will use the adapter class MediaAdapter passing it the desired audio type without knowing the actual class which can play the desired format.adapterpatterndemo, our demo class will use AudioPlayer class to play various formats.

17 Answer 4 (cont)

18 Question 5 (Take 5 minutes) We need to create 3 types of cars: Small, Luxury and Sedans. A car can lie in any one of the above 3 categories. Building a car requires many steps from allocating accessories to final makeup. Depending on the user s request we need to create a type of car. What design pattern would you use to implement this scenario? Can you draw a UML diagram to depict the implementation?

19 Answer 5 : Factory Pattern