在軟體開發中，堅持乾淨的程式碼實踐對於創建可維護、可擴展和高效的應用程式至關重要。鼓勵這種紀律的一種方法是物件體操，這是一組旨在指導開發人員編寫更好的物件導向程式碼的規則。
在這篇文章中，我將探討物件健身操的原理以及如何應用它們來編寫更清晰、更結構化的程式碼。如果您有興趣深入研究實際程式碼範例或了解如何在實際專案中實現這些原則，請隨時查看我的 GitHub 儲存庫以獲取更多詳細資訊。
有關更多實踐說明，請訪問我的 GitHub 儲存庫。
對象健身操是一項程式設計練習，由九個規則組成，鼓勵您遵守物件導向的原則。這些規則本身是由 Jeff Bay 在他的《The ThoughtWorks Anthology》一書中介紹的。目的是透過遵循這些約束來鼓勵更深入地關注程式碼的設計和結構。
以下是 9 條規則：
這個原則規定每個方法應該只有一層縮排。透過保持較低的縮排級別，我們可以提高可讀性並使程式碼更易於維護。如果一個方法有太多級縮排，通常表示內部邏輯太複雜，需要分解成更小的部分。
實作範例
下面是不遵循這個原則的方法範例：
public class OrderService {
public void processOrder(Order order) {
if (order.isValid()) {
if (order.hasStock()) {
if (order.hasEnoughBalance()) {
order.ship();
} else {
System.out.println("Insufficient balance.");
}
} else {
System.out.println("Stock unavailable.");
}
} else {
System.out.println("Invalid order.");
}
}
}
上面的程式碼中，processOrder 方法中存在多層縮進，這使得閱讀起來更加困難，尤其是當邏輯變得更加複雜時。
現在，讓我們看看如何透過簡化邏輯來遵循原則：
public class OrderService {
public void processOrder(Order order) {
if (!isOrderValid(order)) return;
if (!hasStock(order)) return;
if (!hasEnoughBalance(order)) return;
shipOrder(order);
}
private boolean isOrderValid(Order order) {
if (!order.isValid()) {
System.out.println("Invalid order.");
return false;
}
return true;
}
private boolean hasStock(Order order) {
if (!order.hasStock()) {
System.out.println("Stock unavailable.");
return false;
}
return true;
}
private boolean hasEnoughBalance(Order order) {
if (!order.hasEnoughBalance()) {
System.out.println("Insufficient balance.");
return false;
}
return true;
}
private void shipOrder(Order order) {
order.ship();
}
}
此版本每個邏輯區塊都有一級縮進，使程式碼更乾淨且更易於維護。
在物件導向程式設計中，else關鍵字的使用常常會導致程式碼混亂且難以維護。您可以使用提前傳回或多態性來建立程式碼，而不是依賴 else 語句。這種方法增強了可讀性，降低了複雜性，並使您的程式碼更易於維護。
我們先來看一個使用 else 關鍵字的範例：
public class Order {
public void processOrder(boolean hasStock, boolean isPaid) {
if (hasStock && isPaid) {
System.out.println("Order processed.");
} else {
System.out.println("Order cannot be processed.");
}
}
}
在此範例中，else 語句迫使我們明確處理否定情況，從而增加了額外的複雜性。現在，讓我們重構它以避免使用 else：
public class Order {
public void processOrder(boolean hasStock, boolean isPaid) {
if (!hasStock) {
System.out.println("Order cannot be processed: out of stock.");
return;
}
if (!isPaid) {
System.out.println("Order cannot be processed: payment pending.");
return;
}
System.out.println("Order processed.");
}
}
透過消除 else，您可以編寫更有針對性的程式碼，每個部分處理一個職責。這符合“單一職責原則”，有助於創建更乾淨、更易於維護的軟體。
物件健身操的關鍵實踐之一是將所有基元和字串包裝在自訂類別中。此規則鼓勵開發人員避免直接在程式碼中使用原始基元類型或字串。相反，他們應該將它們封裝在有意義的物件中。這種方法使程式碼更具表現力、更易於理解，並且可以增加複雜性，但不會變得難以管理。
讓我們考慮一個直接使用原始類型和字串的範例：
public class Order {
private int quantity;
private double pricePerUnit;
private String productName;
public Order(int quantity, double pricePerUnit, String productName) {
this.quantity = quantity;
this.pricePerUnit = pricePerUnit;
this.productName = productName;
}
public double calculateTotal() {
return quantity * pricePerUnit;
}
}
這段程式碼直接使用了int、double、String。雖然這看起來很簡單，但它並沒有清楚地表達每個值的意圖，並且使得以後引入特定於這些值的新行為或約束變得更加困難。
現在，讓我們重構這段程式碼來包裝原語和字串:
public class Quantity {
private final int value;
public Quantity(int value) {
if (value < 1) {
throw new IllegalArgumentException("Quantity must be greater than zero.");
}
this.value = value;
}
public int getValue() {
return value;
}
}
public class Price {
private final double value;
public Price(double value) {
if (value <= 0) {
throw new IllegalArgumentException("Price must be positive.");
}
this.value = value;
}
public double getValue() {
return value;
}
}
public class ProductName {
private final String name;
public ProductName(String name) {
if (name == null || name.isEmpty()) {
throw new IllegalArgumentException("Product name cannot be empty.");
}
this.name = name;
}
public String getValue() {
return name;
}
}
public class Order {
private final Quantity quantity;
private final Price pricePerUnit;
private final ProductName productName;
public Order(Quantity quantity, Price pricePerUnit, ProductName productName) {
this.quantity = quantity;
this.pricePerUnit = pricePerUnit;
this.productName = productName;
}
public double calculateTotal() {
return quantity.getValue() * pricePerUnit.getValue();
}
}
主要變化：
每當您使用 List 或 Map 等集合時，請將其設為專用物件。這可以使您的程式碼保持乾淨，並確保封裝與集合相關的邏輯。
Problem: Using a Raw Collection Directly
public class Order {
private List<String> items;
public Order() {
this.items = new ArrayList<>();
}
public void addItem(String item) {
items.add(item);
}
public List<String> getItems() {
return items;
}
}
In this example, Order directly uses a List
Solution: Using a First-Class Collection
public class Order {
private Items items;
public Order() {
this.items = new Items();
}
public void addItem(String item) {
items.add(item);
}
public List<String> getItems() {
return items.getAll();
}
}
class Items {
private List<String> items;
public Items() {
this.items = new ArrayList<>();
}
public void add(String item) {
items.add(item);
}
public List<String> getAll() {
return new ArrayList<>(items); // Return a copy to prevent external modification
}
public int size() {
return items.size();
}
}
Explanation:
Benefits of First-Class Collections:
One Dot Per Line is an Object Calisthenics rule that encourages developers to avoid chaining multiple method calls on a single line. The principle focuses on readability, maintainability, and debugging ease by ensuring that each line in the code only contains a single method call (represented by one "dot").
The Problem with Method Chaining (Multiple Dots Per Line)
When multiple methods are chained together on one line, it can become difficult to:
Example: Multiple Dots Per Line (Anti-Pattern)
public class OrderProcessor {
public void process(Order order) {
String city = order.getCustomer().getAddress().getCity().toUpperCase();
}
}
In this example, we have multiple method calls chained together (getCustomer(), getAddress(), getCity(), toUpperCase()). This makes the line of code compact but harder to understand and maintain.
Solution: One Dot Per Line
By breaking down the method chain, we make the code easier to read and debug:
public class OrderProcessor {
public void process(Order order) {
Customer customer = order.getCustomer(); // One dot: getCustomer()
Address address = customer.getAddress(); // One dot: getAddress()
String city = address.getCity(); // One dot: getCity()
String upperCaseCity = city.toUpperCase(); // One dot: toUpperCase()
}
}
This code follows the One Dot Per Line rule by breaking down a method chain into smaller, readable pieces, ensuring that each line performs only one action. This approach increases readability, making it clear what each step does, and improves maintainability by making future changes easier to implement. Moreover, this method helps during debugging, since each operation is isolated and can be checked independently if any errors occur.
In short, the code emphasizes clarity, separation of concerns, and ease of future modifications, which are key benefits of applying Object Calisthenics rules such as One Dot Per Line.
One of the key rules in Object Calisthenics is Don’t Abbreviate, which emphasizes clarity and maintainability by avoiding cryptic or shortened variable names. When we name variables, methods, or classes, it’s important to use full, descriptive names that accurately convey their purpose.
Example of Bad Practice (With Abbreviations):
public class EmpMgr {
public void calcSal(Emp emp) {
double sal = emp.getSal();
// Salary calculation logic
}
}
Example of Good Practice (Without Abbreviations):
public class EmployeeManager {
public void calculateSalary(Employee employee) {
double salary = employee.getSalary();
// Salary calculation logic
}
}
By avoiding abbreviations, we make our code more understandable and maintainable, especially for other developers (or even ourselves) who will work on it in the future.
In Object Calisthenics, one of the fundamental rules is Keep Entities Small, which encourages us to break down large classes or methods into smaller, more manageable ones. Each entity (class, method, etc.) should ideally have one responsibility, making it easier to understand, maintain, and extend.
Example of Bad Practice (Large Class with Multiple Responsibilities):
public class Employee {
private String name;
private String address;
private String department;
public void updateAddress(String newAddress) {
this.address = newAddress;
}
public void promote(String newDepartment) {
this.department = newDepartment;
}
public void generatePaySlip() {
// Logic for generating a payslip
}
public void calculateTaxes() {
// Logic for calculating taxes
}
}
In this example, the Employee class is doing too much. It’s handling address updates, promotions, payslip generation, and tax calculation. This makes the class harder to manage and violates the Single Responsibility Principle.
Example of Good Practice (Small Entities with Single Responsibilities):
public class Employee {
private String name;
private String address;
private String department;
public void updateAddress(String newAddress) {
this.address = newAddress;
}
public void promote(String newDepartment) {
this.department = newDepartment;
}
}
public class PaySlipGenerator {
public void generate(Employee employee) {
// Logic for generating a payslip for an employee
}
}
public class TaxCalculator {
public double calculate(Employee employee) {
// Logic for calculating taxes for an employee
return 0.0;
}
}
By breaking the class into smaller entities, we:
The principle of avoiding getters and setters encourages encapsulation by ensuring that classes manage their own data and behavior. Instead of exposing internal state, we should focus on providing meaningful methods that perform actions relevant to the class's responsibility.
Consider the following example that uses getters and setters:
public class BankAccount {
private double balance;
public double getBalance() {
return balance;
}
public void setBalance(double balance) {
this.balance = balance;
}
public void deposit(double amount) {
balance += amount;
}
public void withdraw(double amount) {
if (amount <= balance) {
balance -= amount;
}
}
}
In this example, the getBalance method exposes the internal state of the BankAccount class, allowing direct access to the balance variable.
A better approach would be to avoid exposing the balance directly and provide methods that represent the actions that can be performed on the account:
public class BankAccount {
private double balance;
public void deposit(double amount) {
balance += amount;
}
public void withdraw(double amount) {
if (amount <= balance) {
balance -= amount;
}
}
public boolean hasSufficientFunds(double amount) {
return amount <= balance;
}
}
In this revised example, the BankAccount class no longer has getters or setters. Instead, it provides methods for depositing, withdrawing, and checking if there are sufficient funds. This approach maintains the integrity of the internal state and enforces rules about how the data can be manipulated, promoting better encapsulation and adherence to the single responsibility principle.
The principle of separating user interface (UI) code from business logic is essential for creating maintainable and testable applications. By keeping these concerns distinct, we can make changes to the UI without affecting the underlying business rules and vice versa.
Consider the following example where the UI and business logic are intertwined:
public class UserRegistration {
public void registerUser(String username, String password) {
// UI Logic: Validation
if (username.isEmpty() || password.length() < 6) {
System.out.println("Invalid username or password.");
return;
}
// Business Logic: Registration
System.out.println("User " + username + " registered successfully.");
}
}
In this example, the registerUser method contains both UI logic (input validation) and business logic (registration). This makes the method harder to test and maintain.
A better approach is to separate the UI from the business logic, as shown in the following example:
public class UserRegistration {
public void registerUser(User user) {
// Business Logic: Registration
System.out.println("User " + user.getUsername() + " registered successfully.");
}
}
public class UserRegistrationController {
private UserRegistration userRegistration;
public UserRegistrationController(UserRegistration userRegistration) {
this.userRegistration = userRegistration;
}
public void handleRegistration(String username, String password) {
// UI Logic: Validation
if (username.isEmpty() || password.length() < 6) {
System.out.println("Invalid username or password.");
return;
}
User user = new User(username, password);
userRegistration.registerUser(user);
}
}
class User {
private String username;
private String password;
public User(String username, String password) {
this.username = username;
this.password = password;
}
public String getUsername() {
return username;
}
}
In this improved design, the UserRegistration class contains only the business logic for registering a user. The UserRegistrationController is responsible for handling UI logic, such as input validation and user interaction. This separation makes it easier to test and maintain the business logic without being affected by changes in the UI.
By adhering to this principle, we enhance the maintainability and testability of our applications, making them easier to adapt to future requirements.
Object Calisthenics might seem a bit strict at first, but give it a try! It's all about writing cleaner, more maintainable code that feels good to work with. So, why not challenge yourself? Start small, and before you know it, you’ll be crafting code that not only works but also shines. Happy coding!
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