package cn.sasa.demo1;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator; public class ListDemo {
public static void main(String[] args) {
//泛型的通配符 ?
Collection<String> strColl = new ArrayList<String>();
Collection<Integer> intColl = new ArrayList<Integer>(); strColl.add("hahaha");
intColl.add(111); //strColl 和 intColl 都可以成为 printColl方法的参数,因为<>里写了通配符?,匹配所有的数据类型
printColl(strColl);
printColl(intColl); //泛型的限定
//如果<>里用?匹配所有的类型,会有安全隐患
//设计一个方法,使其可以调用Dog类的集合和Cat类的集合中元素的speak()方法
Collection<Dog> dogColl = new ArrayList<Dog>();
dogColl.add(new Dog("Wangcai",4));
dogColl.add(new Dog("aHuang",3)); Collection<Cat> catColl = new ArrayList<Cat>();
catColl.add(new Cat("Kittey",6));
catColl.add(new Cat("Ruby",2)); speak(dogColl);
speak(catColl); //Collection<String> testColl = new ArrayList<String>();
//testColl.add("qqq");
//speak(testColl);//报错,因为testColl里的元素不是Animal的子类 }
/**
* 使不同的泛型集合都可以调用这个方法
* 泛型的通配符 ?
*/
static void printColl(Collection<?> coll) {
Iterator<?> it = coll.iterator();
while(it.hasNext()) {
System.out.println(it.next());
}
} /**
* ? extends 限定为某个类的子类
* ? super 限定为某个类的父类
*/
static void speak(Collection<? extends Animal> coll) {
Iterator<? extends Animal> it = coll.iterator();
while(it.hasNext()) {
Animal animal = it.next();
animal.speak();
}
}
}
package cn.sasa.demo1;

public abstract class Animal {
private String type;
private int age;
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
} public abstract void speak();
}
package cn.sasa.demo1;

public class Dog extends Animal{

    public Dog(String type, int age) {this.setType(type);
this.setAge(age);
}
@Override
public void speak() {
System.out.println(this.getType() + " Wang wang");
} }
package cn.sasa.demo1;

public class Cat extends Animal{

    public Cat(String type, int age) {this.setType(type);
this.setAge(age);
}
@Override
public void speak() {
System.out.println(this.getType() + " Mellow mellow");
} }
04-26 17:43
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