- Association
- represent a bi-directional relationship: one student play many sports, a sport can be played by many student
- No ownership: student doesn't own sport
- No lifecycle dependency: If one object is destroyed, the other can continue to exist - If one student stop playing, sport still exist. vice versa
public class Student{
public void play(Sport: sport){
execute.play(sport);
}
}
- Aggregation
- week has-a relationship: a whole has parts that belongs to it
- no lifecycle dependency: exist independent
class Airliner{
private ArrayList<CrewMember> crew;
public Airliner(){
crew = new ArrayList<CrewMember>();
}
public void add(CrewMember crewMember){}
}
- airliner have 0 or many crew members
- can add crew members latter
- Composition
- Strong has-a relationship => access parts through its whole
- Part exclusive belong to whole
- Lifecycle dependency
public class House{
private Room room;
public House(){
room = new Room();
}
}
- room created at the same time with the House
- Dependency
- represent a relationship where change in one class may affect another class
- Doesn't imply structural relationships but rather a reliance
- Car depend on Fuel but NO ownership or direct association
class Car{
public void start(Fuel fuel){}
}
class Fuel{
}
- Intent
- one instance
- provide global access to this instance
- Implement
- private static field for singleton instance
- private constructor
- public static creation method to get instance
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