CPSC 210

Design Review

(last lecture 😢👋)

We have a guest today...

The maker of Lab4 has a new lab to present...

More workspace practice for the final exam!

Mazen

And now...

Teaching

Evaluations

Please

Design Review

From high-level design principles to a sample of concrete design patterns

  • Well-designed software has high cohesion and low coupling
  • Most design patterns improve on cohesion and coupling

Cohesion

Every class should have a
single responsibility

Coupling

Measure how system components depend on each other

Liskov Substitution Principle

  • Design principle that states:
    • when a subtype is substituted for its super type:
      • the subtype must provide the expected behaviours of the super type

Refactoring

  • We refactor our code to improve on:
    • the design of our codebase
    • coupling by abstracting duplicated code
    • cohesion by splitting up classes

Design Patterns

We make mistakes

We identify our mistakes

We learn from our mistakes

We prevent mistakes

We Evolve Design Patterns

Lessons Learned!

Composite

I have a tree structure and I don't know all the types of objects in the tree

Run operations recursively through my tree without knowing the types in my tree

Observer

I want objects to know about a state but I don't know what these objects are

Objects can be added and removed as they desire

Singleton

I want to coordinate a state across my system

There is always exactly one instance of this state in my system

Iterator

I have a collection of elements and there should always be a "next" element

Traverse elements without exposing its implementation

ArrayListIterator<E>
LinkedListIterator<E>
HashSetIterator<E>

Iterable<E>

Iterator<E> iterator()

<<interface>>

Iterator<E>

boolean hasNext()
E next()
void remove()

<<interface>>

Collection

<<interface>>

Design patterns help us with the design of our code base

  • But language design also improves over time
  • Some examples...
Iterator<Item> itr = collection.iterator();
while (itr.hasNext()) {
  Item nextItem = itr.next();
  // do something with nextItem
}

Before Java 5

Since Java 5 (2004)

for (Item next : collection) {
    // do something with next
}
button.addActionListener(new ActionListener() {
  public void actionPerformed(ActionEvent evt) {
    System.out.println("Do something");
  }
});

Before Java 8

button.addActionListener(e -> {
  System.out.println("Do something");
});

Since Java 8 (2014)

List<String> list = new ArrayList<>();
list.add("dog");
list.add("cat");
list.add("hamster");

Before Java 9

List<String> list = List.of(
  "dog", "cat", "hamster");

Since Java 9 (2017)

Map<String, Integer> map = new HashMap<>();
map.put("dog", 1);
map.put("cat", 5);
map.put("hamster", 7);

Before Java 9

Map<String, Integer> map = Map.of(
  "dog", 1, "Cat", 5, "Hamster", 7);

Since Java 9 (2017)

Libraries and Frameworks also help us with design

  • Sometimes it's a good idea to look what's out there to help us write good code!
  • One example... you may want to update your projects... 😉

Lombok

public class User {
  private String firstName;
  private String lastName;
  private int age;
  private String email;

  public User(String firstName, String lastName, 
              int age, String email) {
    this.firstName = firstName;
    this.lastName = lastName;
    this.age = age;
    this.email = email;
  }
  public void setFirstName(String firstName) {
    this.firstName = firstName;
  }
  public void setLastName(String lastName) {
    this.lastName = lastName;
  }
  public void setAge(int age) {
    this.age = age;
  }
  public void setEmail(String email) {
    this.email = email;
  }
  public String getFirstName() {
    return firstName;
  }
  public String getLastName() {
    return lastName;
  }
  public int getAge() {
    return age;
  }
  public String getEmail() {
    return email;
  }
}

https://projectlombok.org/

import lombok.AllArgsConstructor;
import lombok.Data;

@Data
@AllArgsConstructor
public class User {
  private String firstName;
  private String lastName;
  private int age;
  private String email;
}

Sometimes new languages build on other languages

Kotlin

https://kotlinlang.org/

System.out.print("Hello");
System.out.println("Hello");

Java

print("Hello!")
println("Hello!")

Kotlin

final int a;
final int b = 21;
int c;
int d = 25;
d = 23;
c = 21;

Java

val a: Int
val b = 21
var c: Int
var d = 25
d = 23
c = 21

Kotlin

if(str instanceof String){
  String result = ((String) str).substring(1);
}

Java

if (str is String) {
    val result = str.substring(1)
}

Kotlin

You always need to find what works best for you 🤞

Hope you had a good time!
We certainly had! 🎊

This was CPSC 210!

Design Review

By Felix Grund

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Design Review

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