请问以下代码,在哪里体现了“父类引用指向子类对象”
abstract class Animal {
private String name;
Animal(String name) {this.name = name;}
/*
public void enjoy(){
System.out.println("叫声......");
}
*/
public abstract void enjoy();
}abstract class Cat extends Animal {
private String eyesColor;
Cat(String n,String c) {super(n); eyesColor = c;}
/*
public void enjoy() {
System.out.println("猫叫声......");
}
*/
//public abstract void enjoy();
}class Dog extends Animal {
private String furColor;
Dog(String n,String c) {super(n); furColor = c;}
public void enjoy() {
System.out.println("狗叫声......");
}
}class Bird extends Animal {
Bird() {
super("bird");
}
public void enjoy() {
System.out.println("鸟叫声......");
}
}class Lady {
private String name;
private Animal pet;
Lady(String name,Animal pet) {
this.name = name; this.pet = pet;
}
public void myPetEnjoy()
{pet.enjoy();}
}public class Test {
public static void main(String args[]){
Cat c = new Cat("catname","blue");
Dog d = new Dog("dogname","black");
Bird b = new Bird();
//Lady l1 = new Lady("l1",c);
Lady l2 = new Lady("l2",d);
Lady l3 = new Lady("l3",b);
//l1.myPetEnjoy();
l2.myPetEnjoy();
l3.myPetEnjoy();
}
}
abstract class Animal {
private String name;
Animal(String name) {this.name = name;}
/*
public void enjoy(){
System.out.println("叫声......");
}
*/
public abstract void enjoy();
}abstract class Cat extends Animal {
private String eyesColor;
Cat(String n,String c) {super(n); eyesColor = c;}
/*
public void enjoy() {
System.out.println("猫叫声......");
}
*/
//public abstract void enjoy();
}class Dog extends Animal {
private String furColor;
Dog(String n,String c) {super(n); furColor = c;}
public void enjoy() {
System.out.println("狗叫声......");
}
}class Bird extends Animal {
Bird() {
super("bird");
}
public void enjoy() {
System.out.println("鸟叫声......");
}
}class Lady {
private String name;
private Animal pet;
Lady(String name,Animal pet) {
this.name = name; this.pet = pet;
}
public void myPetEnjoy()
{pet.enjoy();}
}public class Test {
public static void main(String args[]){
Cat c = new Cat("catname","blue");
Dog d = new Dog("dogname","black");
Bird b = new Bird();
//Lady l1 = new Lady("l1",c);
Lady l2 = new Lady("l2",d);
Lady l3 = new Lady("l3",b);
//l1.myPetEnjoy();
l2.myPetEnjoy();
l3.myPetEnjoy();
}
}
Animal cat = new Cat("catname", "blue");
cat.enjoy();
就体现了
Lady l2 = new Lady("l2",d);
Lady l3 = new Lady("l3",b);传递的参数 d ,b 声明的是 Cat和Dog类的
Cat c = new Cat("catname","blue");
Dog d = new Dog("dogname","black");传递过去后 是Animal类型的
Lady(String name,Animal pet) {}就是这个地方体现出了“父类引用指向子类对象”
父类引用指向子类对象
必须有方法覆盖
子类的访问修饰符不能比父类更有限制
多态只运用于方法,不适用用数据
多态意味着根据包含在一个方法调用中的对象的实际类型来应该决定调用哪个方法,而不是由用来存储对象引用变量的类型决定。例子中
public abstract void enjoy();//父类方法
public void enjoy() {
System.out.println("狗叫声......");//子类重写了父类的方法
public void enjoy() {
System.out.println("鸟叫声......");
Dog d = new Dog("dogname","black");创建了一个新的Dog对象Lady l2 = new Lady("l2",d);
Lady(String name,Animal pet) {
this.name = name; this.pet = pet;
} //这个构造函数 把父类变量引用指向dog对象。l2.myPetEnjoy(); 这句话根据父类变量引用指向的对象的类型来确定调用哪个方法,也就是dog里面的enjoy方法,是在程序运行的时候动态绑定的如果父类变量引用的是cat对象,就调用cat里面的enjoy方法,如果是bird对象就调用bird里的enjoy方法 。。这就是多态也叫动态绑定又叫池绑定