将特定值注入对象构造函数

public class Person {
    private String name;
    
    public Person(String name) {
        this.name = name;
    }
    
    // ...
}

Person person = new Person("John");

public class DatabaseConnection {
    private String url;
    private String username;
    private String password;
    
    public DatabaseConnection(String url, String username, String password) {
        this.url = url;
        this.username = username;
        this.password = password;
    }
    
    // ...
}

// 从配置文件中读取数据库连接信息
String url = Config.getProperty("db.url");
String username = Config.getProperty("db.username");
String password = Config.getProperty("db.password");

DatabaseConnection connection = new DatabaseConnection(url, username, password);

public class OrderService {
    private OrderRepository orderRepository;
    
    public OrderService(OrderRepository orderRepository) {
        this.orderRepository = orderRepository;
    }
    
    // ...
}

// 使用依赖注入框架（如Spring）配置对象之间的依赖关系
@Bean
public OrderRepository orderRepository() {
    return new OrderRepositoryImpl();
}

@Bean
public OrderService orderService(OrderRepository orderRepository) {
    return new OrderService(orderRepository);
}