我正在上一门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;以及三个子类,每个子类都有自己独特的特性(我选择了"Dog”、"Cat“和"Bird")。在我们构建了所有这些之后,我们将创建一个主类来测试所有东西,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,但它似乎只找到超类中的方法。
下面是主类:
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;
}
}
下面是一个子类(它们看起来都是一样的,都有相同的错误)
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,我无法使用main方法来查找cat.getColor()
方法,也无法找到子类所特有的任何其他方法。
发布于 2012-04-05 09:55:06
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(在本例中为Cat
)中的方法,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
或者将其强制转换为您知道/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
您甚至可以结合使用这两种方法:
Pet pet = new Cat("Feline",12,"Orange");
Cat cat = (Cat)pet;
cat.getName(); // OK
cat.getColor(); // OK
发布于 2012-04-05 09:48:01
Pet cat = new Cat("Feline",12,"Orange");
^^^
This is the error.
Pet
没有名为getColor()
的方法
您需要做的是:
Cat cat = new Cat(...);
发布于 2012-04-05 09:50:33
执行此操作时:
Pet cat = new Cat("Feline",12,"Orange");
编译器将变量cat视为Pet。所以你不能使用Cat类的特定方法。
您必须将cat声明为Type Cat以解决您的问题。
致以问候。
https://stackoverflow.com/questions/10021603
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