从超类调用子类方法

问题描述

我在介绍性的java课程中，我们刚开始学习继承。我正在开展一项任务，要求我们创建一个名字和年龄的Pet超类;和三个子类，每个都有自己独特的特性（我选择了狗，猫和鸟）。在我们构建了所有这些之后，我们将创建一个Main类来测试所有内容，这就是我遇到问题的地方。我试图在 Main 中为这些独特的特征调用 get 方法，但它似乎只找到方法在超类中。

I am in an introductory java course and we just started learning about inheritance. I am working on a task that asks that we create a "Pet" superclass with name and age; and three subclasses, each with their own unique trait (I have chosen "Dog", "Cat", and "Bird"). After we have all these built, we are to create a Main class to test everything, and this is where I am running into problems. I am attempting to call the get methods for these unique traits within Main, but it seems to only find methods that are in the superclass.

这是Main类：

public class Kennel {
    public static void main(String[] args) {
        // Create the pet objects
        Pet cat = new Cat("Feline", 12, "Orange");
        Pet dog = new Dog("Spot", 14, "Dalmation");
        Pet bird = new Bird("Feathers", 56, 12);

        // Print out the status of the animals
        System.out.println("I have a cat named " + cat.getName()
                + ". He is " + cat.getAge() + " years old."
                + " He is " + cat.getColor()
                + "When he speaks he says " + cat.speak());
        System.out.println("I also have a dog named " + dog.getName()
                + ". He is " + dog.getAge() + " years old."
                + " He is a " + dog.getBreed()
                + " When he speaks he says " + dog.speak());
        System.out.println("And Finally I have a bird named "
                + bird.getName() + ". He is " + bird.getAge() + " years old."
                + " He has a wingspan of " + bird.getWingspan() + " inches."
                + " When he speaks he says " + bird.speak());
    }
}

这是我的超类

abstract public class Pet {
    private String name;
    private int age;

    // Constructor
    public Pet(String petName, int petAge) {
        this.name = petName;
        this.age = petAge;
    }

    // Getters
    public String getName() { return(this.name); }
    public int getAge() { return(this.age); }

    // Setters
    public void setName(String nameSet) { this.name = nameSet; }
    public void setAge(int ageSet) { this.age = ageSet; }

    // Other Methods
    abstract public String speak();

    // toString
    @Override
    public String toString() {
        String answer = "Name: " + this.name + " Age: " + this.age;
        return answer;
    }
}

这是其中一个子类（它们都看起来相同并且具有相同的错误）

And here is one of the subclasses (they all look the same and are having the same error)

public class Cat extends Pet {
    private String color;

    // Constructor
    public Cat(String petName, int petAge, String petColor) {
        super(petName, petAge);
        this.color = petColor;
    }

    // Getters
    public String getColor() { return(this.color); }

    // Setters
    public void setColor(String colorSet) { this.color = colorSet; }

    // Other Methods
    @Override
    public String speak() { return "Meow!"; }

    // toString
    @Override
    public String toString() {
        String answer = "Name: " + super.getName() + " Age: "+super.getAge()
                + " Color: " + this.color;
        return answer;
    }
}

所以发生的事情是我无法得到找到 cat.getColor（）方法的主要方法，或者子类特有的任何其他方法。

So what is happening is I can't get the main method to find the cat.getColor() method, or any of the other ones unique to the subclasses.

推荐答案

当您将变量声明为具有超类的类型时，您只能通过该变量访问超类​​的（公共）方法和成员变量。

When you declare a variable as having the type of the superclass, you can only access (public) methods and member variables of the superclass through that variable.

Pet cat = new Cat("Feline",12,"Orange");
cat.getName(); // this is OK
cat.getColor(); // this is not OK, getColor() is not in Pet

访问具体方法class（ Cat 在这种情况下），你需要将变量声明为派生类

To access the methods in the concrete class (Cat in this case), you need to either declare the variable as the derived class

Cat cat = new Cat("Feline",12,"Orange");
cat.getName(); // OK, getName() is part of Cat (and the superclass)
cat.getColor(); // OK, getColor() is part of Cat

或者把它投射到你知道/怀疑的类型具体类型

Or cast it to a type you know/suspect is the concrete type

Pet cat = new Cat("Feline",12,"Orange");
((Cat)cat).getName(); // OK (same as above)
((Cat)cat).getColor(); // now we are looking at cat through the glass of Cat

您甚至可以将这两种方法结合起来：

You can even combine the two methods:

Pet pet = new Cat("Feline",12,"Orange");
Cat cat = (Cat)pet;
cat.getName(); // OK
cat.getColor(); // OK

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