每一个类扩展到类对象，但我的程序给我错误，方法print()没有为对象类型定义

Question

class Aquatic extends Animal {
boolean scale;
Aquatic(long years,float kg, boolean skin){
super(years,kg);
scale=skin;
}
public void print() {
super.print();
System.out.println(scale);
}

}

public class Animal  {
long lifespan;
float weigh;
Animal(long years,float kg){

lifespan=years;
weigh=kg;
}

public void print() {
System.out.println(lifespan);
System.out.println(weigh);
}
}

public class AnimalWorld <T extends Animal>{        //scope of Animal and its sub classes
T[] ListOfAnimals;
AnimalWorld(T[] list){
ListOfAnimals=list;
}

}

public class BoundedWildcardArgumentsDemo {
static void vitality(AnimalWorld<?> animal) {

for(Animal a: animal.ListOfAnimals)
a.print();
System.out.println();
}

static void showSea(AnimalWorld<? super Aquatic> animals) {

for(Object obj: animals.ListOfAnimals) {
obj.print(); // This gives error that "method print is undefined for type object
}
}
public static void main(String args[]) {

Animal unknown=new Animal(40,720);
Animal u[]= {unknown};

AnimalWorld<Animal> uList=new AnimalWorld<>(u);
vitality(uList);
}

}

我的Animal类自然应该继承Object类，因此print()应该为obj定义。甚至当我添加Animal extends Object时，我又得到了同样的错误。根据我对继承的理解，obj应该能够访问print()方法。我错过什么了吗?

Answer 1

您只需在boundedwildcardarumentsdemo类的showSea()方法中更改对象的类型。您必须更改"对象"。到"动物物件">

:

static void showSea(AnimalWorld<? super Aquatic> animals) {        
for(Object obj: animals.ListOfAnimals) {
obj.print(); // This gives error that "method print is undefined for type object
}
}

:后

static void showSea(AnimalWorld<? super Aquatic> animals) {
for(Animal obj: animals.ListOfAnimals) {
obj.print(); // This gives error that "method print is undefined for type object
}
}

对象obj"没有"打印"方法，因此您应该将其设置为抽象父类的类型，为"animal"。