如何使用私有成员 Java 创建一个带有子 class 的工作超级 class

Question

我正在参加一个编码训练营并创建了一个 Superclass "Animal" 和一个 subclass "Lion"。所有变量都是私有变量。

当我尝试传递所需的值时，我收到一条错误消息，指出 Lion 无法解析为类型。这是我在 Whosebug 上提出的第一个问题，如果没有正确遵循正常约定，我们深表歉意。

///动物class与子class狮子///

public class Animal {
    private int numTeeth;
    private boolean spots;
    private int weight;

    public Animal(int numTeeth, boolean spots, int weight) {
        this.setNumTeeth(numTeeth);
        this.setSpots(spots);
        this.setWeight(weight);
    }

    int getNumTeeth() {
        return numTeeth;
    }

    boolean getSpots() {
        return spots;
    }

    int getWeight() {
        return weight;
    }

    public void setNumTeeth(int numTeeth) {
        this.numTeeth = numTeeth;
    }

    public void setSpots(boolean spots) {
        this.spots = spots;
    }

    public void setWeight(int weight) {
        this.weight = weight;
    }

    class Lion extends Animal {
        private boolean maine;
        private String region;
        private int type;

        public Lion(boolean maine, String region, int type) {
            super(numTeeth, spots, weight);
            this.setMaine(maine);
            this.setRegion(region);
            this.setType(type);
        }

        boolean getMaine() {
            return maine;
        }

        String getRegion() {
            return region;
        }

        int getType() {
            return type;
        }

        public void setMaine(boolean maine) {
            this.maine = maine;
        }

        public void setRegion(String region) {
            this.region = region;
        }

        public void setType(int type) {
            this.type = type;
        }

        void showAnimal() {
            System.out.println("The number of teeth is: " + getNumTeeth());
            System.out.println("Does the animal have spots!: " + getSpots());
            System.out.println("The animals weight!: " + getWeight());
            System.out.println("Do the animal have a maine!: " + getMaine());
            System.out.println("The animal is from: " + getRegion());
            System.out.println("The animal is a: " + getType());
        }
    }
}

///我试图传入 "AnimalDetails" 的动物统计数据，这是一个新的 class 文件///

public class AnimalStats {

    public static void main(String[] args) {

        Lion stats = new Lion();
        stats.setMaine(true);
        stats.setNumTeeth(20);
        stats.setRegion("South Africa");
        stats.setSpots(false);
        stats.setType(2);
        stats.setWeight(150);
    }
}

我发现的错误在/Lion stats = new Lion(); / Lion 不能被归类为一个类型

Answer 1

Lion 未声明为静态

为了按照您的方式构建 Lion，Lion 应该是静态内部 class。

Lion 中声明的构造函数不包含 super

的参数

为调用 super 添加参数，或者在调用 super 时在构造函数实现中为 numTeeth、spots 和 weight 提供默认值。

Lion 没有 zero-argument 构造函数

您的代码试图实例化一个没有参数的 Lion。如果你想要一个 zero-argument 构造函数，添加一个并为所有成员设置默认值。

否则，调用您已经定义的构造函数。

类似于：

public class Animal {
    private int numTeeth;
    private boolean spots;
    private int weight;

    public Animal(int numTeeth, boolean spots, int weight) {
        this.setNumTeeth(numTeeth);
        this.setSpots(spots);
        this.setWeight(weight);
    }

    int getNumTeeth() {
        return numTeeth;
    }

    boolean getSpots() {
        return spots;
    }

    int getWeight() {
        return weight;
    }

    public void setNumTeeth(int numTeeth) {
        this.numTeeth = numTeeth;
    }

    public void setSpots(boolean spots) {
        this.spots = spots;
    }

    public void setWeight(int weight) {
        this.weight = weight;
    }

    static class Lion extends Animal {
        private boolean maine;
        private String region;
        private int type;

        public Lion(boolean maine, String region, int type, int numTeeth, boolean spots, int weight) {
            super(numTeeth, spots, weight);
            this.setMaine(maine);
            this.setRegion(region);
            this.setType(type);
        }

        boolean getMaine() {
            return maine;
        }

        String getRegion() {
            return region;
        }

        int getType() {
            return type;
        }

        public void setMaine(boolean maine) {
            this.maine = maine;
        }

        public void setRegion(String region) {
            this.region = region;
        }

        public void setType(int type) {
            this.type = type;
        }

        void showAnimal() {
            System.out.println("The number of teeth is: " + getNumTeeth());
            System.out.println("Does the animal have spots!: " + getSpots());
            System.out.println("The animals weight!: " + getWeight());
            System.out.println("Do the animal have a maine!: " + getMaine());
            System.out.println("The animal is from: " + getRegion());
            System.out.println("The animal is a: " + getType());
        }
    }

    public static void main(String[] args) {
        Lion stats = new Lion(true, "South Africa", 2, 20, false, 150);
    }
}

Answer 2

这是一个嵌套 class 的情况，其中一个外部 class 和一个内部 class。

您必须使用外部 class 来实例化内部 class。

由于没有可用的默认构造函数，您必须在实例化时输入值。

Animal.Lion stats = new Animal(20, false, 150).new Lion(true, "South Africa", 2);

AnimalStats class:

public class AnimalStats {
    public static void main(String[] args) {

        Animal.Lion stats = new Animal(20, false, 150).new Lion(true, "South Africa", 2);
    }
}

注意：此解决方案假设 class Animal 必须保持原样并且只需要修复调用者代码。

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