1. ECE452/CS446/SE464 Design Patterns: Part I Questions A Tutorial by Peter Kim Based on slides prepared by Krzysztof Pietroszek

2. Problem 1 public class GUI { … public void setPerson(Person person) { nameLabel.setText(person.getName()); ageLabel.setText(person.getAge()); } public class Person { protected String name; … public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() {…} public void setAge(int age) {…} } To display Person on GUI, GUI.setPerson(Person) must be invoked explicitly. What design pattern could be used so that changes to Person are more implicitly and “automatically” reflected in GUI and potentially in other classes that are interested in Person? Show a) the design pattern and b) an interaction diagram demonstrating a change in Person

3. Problem 2 ● Assume that you are implementing a file system. The main concepts in a file system are directories and files. A directory may contain several files and directories. Additionally, you would like to treat files and directories in a uniform way as nodes, i.e., you would like to be able to write code that can treat both files and directories using the same interface. ➔ What design pattern could you use to achieve these goals? ➔ Draw a class diagram explaining your design.

4. Problem 3: Java API related What design pattern is java.util.Collections.sort(List, Comparator) method an example of? Draw a class diagram and draw some sample code. package java.util; public interface Comparator { public int compare (Object arg1, Object arg2); … }

5. Problem 4: Java API related Consider the following Java I/O streams, where an indentation represents class inheritance (e.g. FileOutputStream extends OutputStream). OutputStream: the generic output stream. FileOutputStream: output stream for writing to files. FilterOutputStream: takes a regular OutputStream as an input and performs some filtering operations on it. DeflaterOutputStream: performs compression on the input OutputStream. ZipOutputStream: produces a compressed output of “Zip” format. GZIPOutputStream: produces a compressed output of “GZIP” format. What design pattern is evident (hint: FilterOutputStream)? Draw a class diagram and provide a sample code.

6. Problem 5 a) A commonly cited advantage of the Decorator design pattern is that it avoids subclass explosion. Explain this using an example. b) Commonly cited disadvantages of the Decorator design pattern are that it allows i) identity crisis and ii) interface occlusion. Why are these problems not evident with subclassing? Explain these using an example.