Question

嗨，大家好我在创建子类的实例时遇到了麻烦：

    package room;

    public class Room {

    String roomNumber;  
    int capacity;
    boolean projection;

    public Room(String rm, int n, boolean p) { 
        roomNumber = rm; 
        capacity = n;
        projection = p;
    }

    public String getRoomNumber() {
        return roomNumber;
    }

    public int getCapacity() {
        return capacity;
    }

    public boolean hasProjector() { 
        return projection;
    }


    public class ComputerLab extends Room {

    private String os;

    public ComputerLab(String rm, int n, boolean p, String os) {
        super(rm, n, p);
        this.os = os;
}

    public String getOS() {
        return os;
    }

    public void setOS(String update) {
        os = update;
    }

}

    public static void main(String[] args) {
        Room r;
        r = new ComputerLab("G102", 20, true, "WindowsXP"); 
        System.out.println(r.getCapacity());
    }
}

在我在main函数中创建ComputerLab对象的行中，我收到以下错误：

Exception in thread "main" java.lang.RuntimeException: Uncompilable source code - non-static variable this cannot be referenced from a static context
    at room.Room.main(Room.java:48)

任何人都可以帮忙解释为什么会出现此错误以及如何解决此问题？非常感谢

Answer 1

您的班级ComputerLab是一个内部班级。在java中，内部类需要封闭类的实例 - 但是main()中没有它（它是静态方法）。

尝试将内部类更改为static - 这意味着它不需要外部类的实例，方法是更改定义：

public class ComputerLab extends Room

到

public static class ComputerLab extends Room

Answer 2

因为你的内部类不是静态的，所以它需要一个周围类的实例。虽然有一种解决方法，但我相信您期望的行为将来自更像这样的代码。

public class Room {

    protected String roomNumber;
    protected int capacity;
    protected boolean projection;

    public Room(String rm, int n, boolean p) {
        roomNumber = rm;
        capacity = n;
        projection = p;
    }

    public String getRoomNumber() {
        return roomNumber;
    }

    public int getCapacity() {
        return capacity;
    }

    public boolean hasProjector() {
        return projection;
    }

    public static void main(String[] args) {
        Room r = new ComputerLab("G102", 20, true, "WindowsXP");
        System.out.println(r.getCapacity());
    }
}

class ComputerLab extends Room {

    private String os;

    public ComputerLab(String rm, int n, boolean p, String os) {
        super(rm, n, p);
        this.os = os;
    }

    public String getOS() {
        return os;
    }

    public void setOS(String update) {
        os = update;
    }

}

Answer 3

尝试

new Room(...).new ComputerLab(...)

Answer 4

你的内部类应该是静态的，就像这样使用它。对嵌套类的良好使用与给定嵌套类的辅助类一样。

我个人喜欢将你的课程分成不同的文件。

Answer 5

您可以在ComputerLab类的声明中添加static：

public static class ComputerLab extends Room ...

Java创建子类错误的实例

5 个答案: