SpringBoot之为何推荐使用构造器注入

/**
 * [ 计算机 ]
 *
 * @author Kareza
 * @time 2021/5/25 10:58 上午
 * @since 1.8
 */
@Component
public class Computer {
    /**
     * 上网
     */
    public void surfInternet(String user) {
        Console.log("{} 正在上网冲浪", user);
    }
}

/**
 * [ 房间 ]
 * @author Kareza
 * @since 1.8
 * @time 2021/5/25 11:42 上午
 */
@Service
public class Room {

    @Autowired
    private Computer computer;

    /**
     * 书房
     */
    public void schoolroom() {
        Console.log("书房里～～");
        // 网上冲浪
        computer.surfInternet("chenyiqiang");
    }
}

Room room = new Room();
room.schollroom(); // -> NullPointerException

/**
 * [ 房间 ]
 * @author Kareza
 * @since 1.8
 * @time 2021/5/25 11:42 上午
 */
@Service
public class Room {

    private Computer computer;

    @Autowired
    public void setComputer(Computer computer) {
        this.computer = computer;
    }

    /**
     * 书房
     */
    public void schoolroom() {
        Console.log("书房里～～");
        // 网上冲浪
        computer.surfInternet("chenyiqiang");
    }
}

/**
 * [ 房间 ]
 * @author Kareza
 * @since 1.8
 * @time 2021/5/25 11:42 上午
 */
@Service
public class Room {

    private final Computer computer;

    @Autowired
    public Room(Computer computer) {
        this.computer = computer;
    }

    /**
     * 书房
     */
    public void schoolroom() {
        Console.log("书房里～～");
        // 网上冲浪
        computer.surfInternet("chenyiqiang");
    }
}