java 使用foreach遍历集合元素的实例

import java.util.*;  public class ForeachTest {   public static void main(String[] args)   {     // 创建集合、添加元素的代码与前一个程序相同     Collection books = new HashSet();     books.add(new String("book1"));     books.add(new String("book2"));     books.add(new String("book3"));     for (Object obj : books)     {       // 此处的book变量也不是集合元素本身       String book = (String)obj;       System.out.println(book);       if (book.equals("book2"))       {         // 下面代码会引发ConcurrentModificationException异常         //books.remove(book);   //①       }     }     System.out.println(books);   } } 

book2book1book3[book2, book1, book3]