通用集合遍历 泛型通配符

创建Person父类

package com.oracle.demo02;

public class Person {
    private String name;
    private int age;
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

    public Person() {
        super();
    }
    public Person(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }
    @Override
    public String toString() {
        return "Person [name=" + name + ", age=" + age + "]";
    }
    public void work() {
        System.out.println("吃饭");
    }
}

创建Student子类

package com.oracle.demo02;

import java.util.ArrayList;
//泛型类
public class Student extends Person{public Student (String name,int age) {
        super(name,age);
    }
    public void work() {
        System.out.println("学习");
    }
}

创建Worker子类

package com.oracle.demo02;

public class Worker extends Person{
    public Worker(String name,int age) {
        super(name,age);
    }
    public void work() {
        System.out.println("工作");
    }
}

测试类

package com.oracle.demo02;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;

public class Demo01 {
    public static void main(String[] args) {

        ArrayList<Student> arr=new ArrayList<Student>();
        arr.add(new Student("小红", 18));
        arr.add(new Student("小蓝", 18));

        HashSet<Worker> brr=new HashSet<Worker>();
        brr.add(new Worker("小红帽", 18));
        brr.add(new Worker("小蓝帽", 18));

        ArrayList<Person> crr=new ArrayList<Person>();
        crr.add(new Person("小小", 18));

        get(arr);
        get(brr);
        get(crr);
    }
    //通用的遍历集合的方法
    public static void get(Collection<? extends Person> col) {
        //  ?  泛型通配符
        //泛型里没有多态，只能用限定符限定
        // 泛型限定符      ? extends  E（父类名称）-->   设置上限（最大父类）
        // 泛型限定符      ? super  E（父类名称） -->  设置下限（最小父类）

        Iterator<?> it=col.iterator();

        while (it.hasNext()) {
            Person p=(Person)it.next();
            p.work();
            break;
        }
    }
}

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原文地址：https://www.cnblogs.com/l1314/p/12108990.html