程序员练级攻略：软件设计-[2026重制版]

// ❌ 违反SRP：User类承担了太多职责
public class User {
    private String name;
    private String email;
 
    public void saveToDatabase() { /* ... */ }
    public void sendEmail() { /* ... */ }
    public void generateReport() { /* ... */ }
    public void validateInput() { /* ... */ }
}
 
// ✅ 遵循SRP：每个类只有一个职责
public class User { // 只负责数据
    private final String name;
    private final String email;
    // getters...
}
 
public class UserRepository { // 只负责持久化
    public void save(User user) { /* ... */ }
}
 
public class EmailService { // 只负责邮件
    public void sendWelcomeEmail(User user) { /* ... */ }
}

// ❌ 违反OCP：每次新增折扣类型都要修改原类
public class DiscountCalculator {
    public double calculateDiscount(String type, double price) {
        switch (type) {
            case "STUDENT": return price * 0.8;
            case "SENIOR": return price * 0.85;
            case "VIP": return price * 0.7;
            default: return price;
        }
    }
}
 
// ✅ 遵循OCP：通过扩展而非修改
public interface DiscountStrategy {
    double calculate(double originalPrice);
}
 
record StudentDiscount() implements DiscountStrategy {
    public double calculate(double price) { return price * 0.8; }
}
 
record VipDiscount() implements DiscountStrategy {
    public double calculate(double price) { return price * 0.7; }
}
 
// 新增折扣类型只需实现接口，无需修改现有代码
class NewYearDiscount implements DiscountStrategy {
    public double calculate(double price) { return price * 0.65; }
}

// ❌ 违反LSP：正方形不能替换长方形
class Rectangle {
    protected int width, height;
    public void setWidth(int w) { this.width = w; }
    public void setHeight(int h) { this.height = h; }
    public int getArea() { return width * height; }
}
 
class Square extends Rectangle {
    @Override
    public void setWidth(int w) {
        super.setWidth(w);
        super.setHeight(w);  // 正方形宽高必须相等！
    }
    @Override
    public void setHeight(int h) {
        super.setHeight(h);
        super.setWidth(h);
    }
}
 
// 使用Rectangle的地方传入Square会出问题！
void test(Rectangle r) {
    r.setWidth(5);
    r.setHeight(10);  // 如果r是Square，宽度也被改成10了！
    assert r.getArea() == 50;  // 失败！实际面积100
}

// ❌ 违反ISP：大而全的接口
interface Worker {
    void work();
    void eat();
    void code();
    void test();
    void manage();
}
 
// ✅ 遵循ISP：小而精的接口
interface Workable {
    void work();
}
 
interface Feedable {
    void eat();
}
 
interface Codeable {
    void code();
}
 
class Developer implements Workable, Feedable, Codeable {
    public void work() { /* ... */ }
    public void eat() { /* ... */ }
    public void code() { /* ... */ }
}
 
class Robot implements Workable, Codeable {
    public void work() { /* ... */ }
    public void code() { /* ... */ }
    // Robot不需要eat()
}