Code-Sharing für generische Qualifizierung in Java

package newFeatures8;
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<String> al = new ArrayList<String>();
		 * 
		 * al.add("abc1"); al.add("abc2"); al.add("abc3");
		 * 
		 * ArrayList<Integer> al1 = new ArrayList<Integer>(); al1.add(4);
		 * al1.add(7); al1.add(1);
		 * 
		 * printColl(al); printColl(al1);
		 */
		//ArrayList<Person> al = new ArrayList<Student>();error
		//为了解决等号两边泛型不一致的情况，jdk1.7以后可以这么写
		ArrayList<Person> al = new ArrayList<>();//右边的泛型自动反射进来
		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); 
	}
	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)
	{
		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<Person> { 
	 public int compareTo(Person s){ 
	 	this.getName() 
	 }
 }
 */
/*
 class Comp implements Comparator<Person>{ //<? super E> 
	 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());//TreeSet(Comparator<? super E> comparator) 
 ts.add(new Student("abc1"));
 ts.add(new Student("abc2"));
 ts.add(new Student("abc3"));
 */