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package Generic;

import java.util.ArrayList;

import java.util.Collection;

import java.util.HashSet;

import java.util.Iterator;

public class Demo9 {

public static void main(String[] args) {

ArrayList<Object> arr = new ArrayList<Object>();

arr.add(new Object());

arr.add("String");

print(arr);

//将集合的泛型设置类String类型，是Object子类

HashSet<String> hs = new HashSet<String>();

hs.add("hello");

hs.add("jack");

//由于print方法接收的集合进行了元素限定，只接受限定为Object类型的集合,编译不通过

print(hs);

}

public static void print(Collection<?> coll) {

Iterator<?> it = coll.iterator();

while (it.hasNext()) {

Object next = it.next();

System.out.println(next);

}

}

}