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依赖注入是一种设计原则,主要用于减少类之间的紧耦合度,通过将对象的选择和创建逻辑外包给一个容器来实现动态注入。
适用场景:
- 当需要将对象的生命周期管理和依赖关系外包给外部容器时(如Spring DI容器)。
- 当应用程序希望通过配置文件或注解来动态更改对象依赖时。
@Component public class Circle implements Shape {@Overridepublic void draw() {System.out.println("Drawing a Circle");} }@Component public class Square implements Shape {@Overridepublic void draw() {System.out.println("Drawing a Square");} }public class ShapeService {private final Shape shape;@Autowiredpublic ShapeService(Shape shape) {this.shape = shape;}public void drawShape() {shape.draw();} }public class Main {public static void main(String[] args) {ApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);ShapeService service = context.getBean(ShapeService.class);service.drawShape(); // 根据Spring配置或XML定义的Shape类型输出} }