UML

1. Class Notation

2. Generalization & Realization

public class A extends B { ... }

public class A implements B { ... }

3. Dependency & Association

[reference], [reference2]

3.0 Cardinality

In UML, cardinality is used to specify the number of instances of one class that can be associated with the instances of another class in an association.

Here are the different cardinality options and what they mean:

• 1: Indicates that there can be only one instance of the associated class.
• 0..1: Indicates that there can be zero or one instance of the associated class.
• 1..* or 1..n: Indicates that there can be one or more instances of the associated class.
• 0..* or * or n..*: Indicates that there can be zero or more instances of the associated class.
• m..n: Indicates that there can be a minimum of m instances and a maximum of n instances of the associated class.
• 1..1: Indicates that there must be exactly one instance of the associated class. This is the same as cardinality of 1.
• 0..0: Indicates that there can be no instances of the associated class.
• n..n: Indicates that there must be exactly n instances of the associated class. This is the same as cardinality of n.

3.1 Dependency

Dependency in UML represents a relationship between two elements where one element, called the dependent element, relies on the other element, called the supplier element, in some way.

public class Car {
  private Engine engine;

  public Car() {
    engine = new Engine();
  }

  public void start() {
    engine.start();
  }
}

public class Engine {
  public void start() {
    // start the engine
  }
}

In this example, the Car class depends on the Engine class, since it needs an instance of Engine to start.

3.2 Association

Association in UML represents a relationship between two elements where one element, called the source element, is related to the other element, called the target element, in some way.

3.2.1 Reflexive Association

public class Company {
  private Set<Person> employees;
  ....
}

public class Person {
  private Company company;
  ...
}

In this example, Company has a set of Persons, and Person has a Company.

3.2.2 Directed Association

public class Company {
  private Set<Person> employees;
  ....
}

public class Person {
  ...
}

In this example, Company has a set of Persons, and Person does not have a Company.

4. Aggregation & Composition

I will update this part soon, please keep an eye on this note and check back for the latest version 👀