classDiagramv0.9.4

クラスとは？

オブジェクト指向の関係と継承。

エディターで開く →すぐに使えるテンプレート

classDiagram

使いどころ

Use a クラス when…

Object-oriented domain modeling

API client/server contracts

Inheritance and composition diagrams

構文の基本

The minimal syntax

Copy this and you have a working クラス. Build from here.

class.mmd

classDiagram
    class User {
      +UUID id
      +string email
      +login()
      +logout()
    }
    class Org {
      +UUID id
      +string name
    }
    class Session {
      +string token
      +revoke()
    }
    User class="code-str">"1" -- class="code-str">"*" Session : owns
    Org class="code-str">"1" -- class="code-str">"*" User : employs

よく使うパターン

Patterns worth memorizing

Visibility prefixes

`+` public, `-` private, `#` protected, `~` package — exactly like UML.

Cardinality

`User "1" -- "*" Post : writes` — quoted multiplicities flank the relation.

Generics

`class List~T~` renders the angle brackets; useful for typed collections.

ハマりどころ

The things that will trip you up

Mermaid silently ignores misspellings — these are the failures we see most.

01
Method bodies aren't supported — only signatures.
02
The relation arrow direction matters: `<|--` is inheritance pointing to the parent.
03
Notes attach to a class with `note for ClassName "text"`.