?不明确类型，占位符

import java.util.ArrayList;

 import java.util.Iterator;



 public class Gener {

 public static void main(String[] args) {

ArrayList<String> al=new ArrayList<String>();

al.add("java1");

al.add("java2");

printCom(al);

ArrayList<Integer> ale=new ArrayList<Integer>();

ale.add(1);

ale.add(2);

printCom(ale);

 }

 /*?不明确类型，占位符

  * 方法内不能使用

  * 

  * public static void printCom(ArrayList<?> al){

for(Iterator<?> it=  al.iterator();it.hasNext();){

  System.out.println(it.next());

 }

 }*/



 public static  <T> void printCom(ArrayList<T> al){

for(Iterator<T> it=  al.iterator();it.hasNext();){

 T t=it.next();

System.out.println(t);

 }

 }

 }