从超类调用子类方法

Question

我正在学习java入门课程，我们刚刚开始学习继承。我正在做一项任务，要求我们创建一个具有名称和年龄的“Pet”超类；和三个子类，每个都有自己独特的特征（我选择了“狗”、“猫”和“鸟”）。在我们构建了所有这些之后，我们将创建一个主类来测试一切，这就是我遇到问题的地方。我试图为这些独特的特性调用get方法，但它似乎只找到超类中的方法。

以下是主要课程：

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;
    }
}

所以现在的情况是，我无法找到找到猫的主要方法。getColor（）方法，或子类特有的任何其他方法。




Answer 1

执行此操作时：

 Pet cat = new Cat("Feline",12,"Orange");

编译器将变量cat视为Pet。因此，您不能使用Cat类的特定方法。

您必须将cat声明为Type Cat才能解决问题。

当做

Answer 2

Pet cat = new Cat("Feline",12,"Orange");
^^^
This is the error.

Pet没有名为getColor（）的方法

你需要做：

Cat cat = new Cat(...);

Answer 3

当您声明一个变量具有超类的类型时，您只能通过该变量访问超类的（公共）方法和成员变量。

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

要访问具体类中的方法（在本例中为Cat），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

或者把它浇铸成你知道/怀疑是混凝土类型的类型

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