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? Class Diagram Tutorial

A Class Diagram is a UML static structure diagram that illustrates the structure of a system through classes, attributes, methods, and their relationships. It serves to visualize system blueprints, aid in object-oriented design, and assist in code generation and database modeling. The document includes examples of class diagrams for an e-commerce system, detailing classes like Customer, Order, and Product, along with their attributes and relationships.

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7 views

? Class Diagram Tutorial

A Class Diagram is a UML static structure diagram that illustrates the structure of a system through classes, attributes, methods, and their relationships. It serves to visualize system blueprints, aid in object-oriented design, and assist in code generation and database modeling. The document includes examples of class diagrams for an e-commerce system, detailing classes like Customer, Order, and Product, along with their attributes and relationships.

Uploaded by

bai598164
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Class Diagram Tutorial (UML)

What is a Class Diagram?


A Class Diagram is a type of static structure diagram in UML that describes the structure of a
system by showing:

• Classes
• Attributes (data members)
• Methods (functions or operations)
• Relationships between classes

Purpose of a Class Diagram


• To visualize the blueprint of a system.
• To show object-oriented design clearly.
• Helps in code generation and reverse engineering.
• Useful in database modeling.

Components of a Class Diagram


Component Description
Class Represents a blueprint of objects.
Attributes The data/fields a class holds.
Methods The behaviors/functions of the class.
Relationships How classes are connected (association, inheritance, etc.).

Class Box Notation


+------------------------+
| Class Name |
+------------------------+
| - attribute1: Type |
| - attribute2: Type |
+------------------------+
| + method1(): ReturnType|
| + method2(arg): void |
+------------------------+
Symbols:

• + Public
• - Private
• # Protected

Example Class: Student


+----------------------+
| Student |
+----------------------+
| - name: String |
| - age: int |
+----------------------+
| + enroll(): void |
| + getDetails(): String |
+----------------------+

Relationships in Class Diagrams


Relationship Symbol/Notation Description
Association Line Basic connection
Inheritance (Generalization) Line with triangle One class is a subclass of another
Aggregation Line with white diamond "Has-a" relationship (weak)
Composition Line with black diamond "Owns-a" relationship (strong)
Dependency Dotted line with arrow Uses temporarily

Example: E-Commerce System


Classes:
• Customer
• Order
• Product

Relationships:

• A Customer places an Order


• An Order contains multiple Products
Text Representation
Customer
---------
- name: String
- email: String
+ placeOrder()

Order
---------
- orderId: int
- date: Date
+ addProduct()

Product
---------
- productId: int
- name: String
+ getPrice()

Relationships:

• Customer → Order: Association


• Order → Product: Composition (Order owns Product details at that time)

Class Diagram

• .
Classes in the Diagram
1. Customer

• Attributes:
o name: String
o email: String
• This class represents the users who place orders on the system.

2. Order

• Attributes:
o orderId: int
o date: Date
• Represents a customer's purchase order.
• An order is made by a customer and may include multiple products.

3. Product

• Attributes:
o productID: int
o name: String
• Represents a product that can be included in one or more orders.

Relationships
Association & Multiplicity

• Customer → Order
There is a line connecting Customer to Order with a diamond and a *:
o This shows a one-to-many relationship.
o One customer can place many orders.
o The diamond indicates aggregation (a customer "has" orders, but orders can exist
independently).
• Order → Product
o There's also a line from Order to Product.
o Suggests that an order contains multiple products.
o This could also be an aggregation (or even composition, if products are
considered part of an order).

Summary in Simple Terms


• A Customer can place many Orders.
• An Order contains many Products.
• The diagram models the real-world structure of an online store's database.

Code
Product.java
public class Product {

private int productID;

private String name;

public Product(int productID, String name) {

this.productID = productID;

this.name = name;

// Getters and Setters

public int getProductID() {

return productID;

public void setProductID(int productID) {

this.productID = productID;

public String getName() {

return name;

public void setName(String name) {

this.name = name;

}
Order.java

import java.util.Date;

import java.util.List;

public class Order {

private int orderId;

private Date date;

private List<Product> products;

public Order(int orderId, Date date, List<Product> products) {

this.orderId = orderId;

this.date = date;

this.products = products;

// Getters and Setters

public int getOrderId() {

return orderId;

public void setOrderId(int orderId) {

this.orderId = orderId;

public Date getDate() {

return date;

public void setDate(Date date) {


this.date = date;

public List<Product> getProducts() {

return products;

public void setProducts(List<Product> products) {

this.products = products;

public void addProduct(Product product) {

this.products.add(product);

Customer.java

java
CopyEdit
import java.util.List;

public class Customer {


private String name;
private String email;
private List<Order> orders;

public Customer(String name, String email, List<Order> orders) {


this.name = name;
this.email = email;
this.orders = orders;
}

// Getters and Setters


public String getName() {
return name;
}

public void setName(String name) {


this.name = name;
}

public String getEmail() {


return email;
}

public void setEmail(String email) {


this.email = email;
}

public List<Order> getOrders() {


return orders;
}

public void setOrders(List<Order> orders) {


this.orders = orders;
}

public void placeOrder(Order order) {


this.orders.add(order);
}
}

🛠 Optional: Main.java to test the setup


java
CopyEdit
import java.util.*;

public class Main {


public static void main(String[] args) {
Product p1 = new Product(101, "Laptop");
Product p2 = new Product(102, "Mouse");

List<Product> productList = new ArrayList<>();


productList.add(p1);
productList.add(p2);

Order order = new Order(1, new Date(), productList);

List<Order> orderList = new ArrayList<>();


orderList.add(order);

Customer customer = new Customer("Alice", "[email protected]",


orderList);

System.out.println("Customer: " + customer.getName());


System.out.println("Orders: " + customer.getOrders().size());
}
}

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