java - 错误 : No enclosing instance of type Main is accessible. 必须使用 Main 类型的封闭实例来限定分配(例如 x.new A() wh

Question

我的代码不起作用。我收到以下错误:

No enclosing instance of type Main is accessible. Must qualify the allocation with an enclosing instance of type Main (e.g. x.new A() where x is an instance of Main).

您可以在下面看到我的代码:

class Main {

public class Room {
    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + etage;
        result = prime * result + gebäude;
        result = prime * result + raumnummer;
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Room other = (Room) obj;
        if (etage != other.etage)
            return false;
        if (gebäude != other.gebäude)
            return false;
        if (raumnummer != other.raumnummer)
            return false;
        return true;
    }

    public int gebäude;
    public int etage;
    public int raumnummer;

    public Room(int gebäude, int etage, int raumnummer) {
        super();
        this.gebäude = gebäude;
        this.etage = etage;
        this.raumnummer = raumnummer;
    }

    @Override
    public String toString() {
        String s = String.format("%2s-%s.%02d", this.gebäude, this.etage, this.raumnummer);
        return s;
    }
}

public static void main(String[] args) {
    Room office = new Room(17, 0, 10);
    Room lecture = new Room(2, 0, 10);
    Room lab = new Room(18, 1, 1);

    System.out.println(office);  // => "17-0.10"
    System.out.println(lecture); // => " 2-0.10"
    System.out.println(lab);     // => "18-1.01"
}

}

Answer 1

解决方案 1

将 Room 类与 Main 类分开对我来说很有效:

文件Main.java:

public class Main {

public static void main(String[] args) {
    Room office = new Room(17, 0, 10);
    Room lecture = new Room(2, 0, 10);
    Room lab = new Room(18, 1, 1);

    System.out.println(office);  // => "17-0.10"
    System.out.println(lecture); // => " 2-0.10"
    System.out.println(lab);     // => "18-1.01"
}
}

文件室.java:

public class Room {
    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + etage;
        result = prime * result + gebäude;
        result = prime * result + raumnummer;
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Room other = (Room) obj;
        if (etage != other.etage)
            return false;
        if (gebäude != other.gebäude)
            return false;
        if (raumnummer != other.raumnummer)
            return false;
        return true;
    }

    public int gebäude;
    public int etage;
    public int raumnummer;

    public Room(int gebäude, int etage, int raumnummer) {
        super();
        this.gebäude = gebäude;
        this.etage = etage;
        this.raumnummer = raumnummer;
    }

    @Override
    public String toString() {
        String s = String.format("%2s-%s.%02d", this.gebäude, this.etage, this.raumnummer);
        return s;
    }
}

让我调查一下为什么会发生这种情况，然后我会发布原因。到目前为止，如果您不需要两个类位于同一个文件中，那么这是一个合适的修复。

解决方案2

使房间静态:

...
class Main {

public static class Room {
    @Override
    public int hashCode() {
        final int prime = 31;
...

为什么会发生这种情况

如 this post 中所述，通过将 Room 作为 Main 的内部类，您将强制 Room 的实例拥有 Main 的实例。当在内部类 Room 上使用 new 运算符而不创建 Main 的新实例时，会产生错误。

通过将 Room 类设为静态，该类不需要 Main 的实例。