Created: 2023-08-28 10:04
Status: #concept
Subject: Programming
Tags: Java Java Class UML

Class Diagram

It is a programmatically generated visual notation to represent Java Class structures.

it describes class attributes, constructors, and method contracts, and the connections between other classes, but not the underlying implementation.

Syntax

UML Class Diagram Cheatsheet.png

a + means the public keyword is used, otherwise - denotes private.
arrows -> represent semantic relationships, for example Book -> Person means a Book class keeps a reference of the Person who wrote the book, but Person doesn't.
an arrow with an asterisk ->* indicates a One-to-many relationship, so the origin class has an ArrayList of the class it points to.
if there is no arrow -, then both classes keep track of a reference of each other.

If a subclass extends a superclass, we represent that relationship with a hollow triangle arrowhead child -|> parent.

if we inherit a Java Abstract Class, we add the <<abstract>> italic label on top of the class name and make all its abstract methods italic.
similarly, when implementing Java Interfaces, we use the same notation but with <<interface>> on top of the class name and a dashed arrow - -|>.

UML Class Diagram Inheritance.png

Some examples of common functions in a Person class:

+Person(name: String) - the Java Class constructor.
-name: String a private attribute.
+sayHi(): void - a public Method that takes in noting & returns nothing.
+getName(): String - a getter method that returns the this.name instance variable.
+setName(String) - a setter method to change this.name of the instance.