java;">package newFeatures8;import java.util.*;/*? 通配符。也可以理解為占位符。泛型的限定；？ extends E: 可以接收E類型或者E的子類型。上限。？ super E: 可以接收E類型或者E的父類型。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		//為了解決等號兩邊泛型不一致的情況，jdk1.7以后可以這么寫		ArrayList<Person> al = new ArrayList<>();//右邊的泛型自動反射進來		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")); */