UML: Class Diagram

Class

1. Normal Class

2. Abstract Class

There are two ways to show an abstract class, use a italicized class name or use {abstract} property:

An abstract can have attributes and abstract methods, and it cannot have implemented methods. We can use abstract classs to achieve code reusability:

3. Interface

An interface can only have abstract methods, and it cannot have attributes and implemented methods. We can use interface to achieve loose coupling:

Relations

1. Generalization: A class can generalize(or inherit from) a superclass or an abstract class.

2. Realization(Implementation): A class can implement an interface.

3. Dependency and association:

public class A {
    private C c;// A has-a C object as a member variable, this is called association.
    
    // A references B (as a method parameter or return type), this is called dependency.
    public void foo(B b) {
        b.callMethod();
    }
}

Note that association can be directed or undirected(in practice we normally use undirected association, namely we do not use an arrow):

4. Aggregation and Composition: