java - 从父类(super class)调用子类方法

Question

我正在学习 Java 入门类(class)，我们刚刚开始学习继承。我正在处理一项任务，要求我们创建一个带有名称和年龄的“宠物”父类(super class)；和三个子类，每个子类都有自己独特的特征(我选择了“狗”、“猫”和“鸟”)。在我们构建完所有这些之后，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，但它似乎只能找到父类(super class)中的方法。

这是主类:

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());       
    }
}

这是我的父类(super class)

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;
    }
}

这是其中的一个子类(它们看起来都一样，并且有相同的错误)

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通过 main 方法找到 cat.getColor() 方法，或任何其他子类独有的方法。

Answer 1

当你声明一个变量具有父类(super class)的类型时，你只能通过这个变量访问父类(super class)​​的(公共(public))方法和成员变量。

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

要访问具体类(本例中为 Cat)中的方法，您需要将变量声明为派生类

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

或将其转换为您知道/怀疑是具体类型的类型

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:

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