Java基础视频教程第15天-12-集合框架(泛型限定)

import java.util.*;
/*
? 通配符。也可以理解为占位符。
泛型的限定；
？ extends E: 可以接收E类型或者E的子类型。上限。
？ super E: 可以接收E类型或者E的父类型。下限

*/


class GenericDemo6
{
    public static void main(String[] args)
    {
        /*
        ArrayList al = new ArrayList();

        al.add("abc1");
        al.add("abc2");
        al.add("abc3");

        ArrayList al1 = new ArrayList();
        al1.add(4);
        al1.add(7);
        al1.add(1);

        printColl(al);
        printColl(al1);
        */

        ArrayList<Person> al = new ArrayList<Person>();
        al.add(new Person("abc1"));
        al.add(new Person("abc2"));
        al.add(new Person("abc3"));
        //printColl(al);

        ArrayList<Student> al1 = new ArrayList<Student>();
        al1.add(new Student("abc--1"));
        al1.add(new Student("abc--2"));
        al1.add(new Student("abc--3"));
        printColl(al1); //ArrayList al = new ArrayList();error

    }
    public static void printColl(Collection<? extends Person> al)
    {
        Iterator<? extends Person> it = al.iterator();


        while(it.hasNext())
        {
            System.out.println(it.next().getName());
        }
    }
    /*
    public static void printColl(ArrayList al)//ArrayList al = new ArrayList();error
    {
        Iterator it = al.iterator();


        while(it.hasNext())
        {
            System.out.println(it.next().toString());
        }
    }
    */
}

class Person
{
    private String name;
    Person(String name)
    {
        this.name = name;
    }
    public String getName()
    {
        return name;
    }
}

class Student extends Person
{
    Student(String name)
    {
        super(name);
    }

}


/*

class Student implements Comparable//
{
    public int compareTo(Person s)
    {
        this.getName()
    }
}
*/
class Comp implements Comparator<Person>
{
    public int compare(Person s1,Person s2)
    {

        //Person s1 = new Student("abc1");
        return s1.getName().compareTo(s2.getName());
    }
}

TreeSet<Student> ts = new TreeSet<Student>(new Comp());
ts.add(new Student("abc1"));
ts.add(new Student("abc2"));
ts.add(new Student("abc3"));