?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);

}

}

}