Java迭代在集合 [英] Java Iterate Over Collection
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问题描述
我有一个练习项目,我需要帮助。这是一个简单的MailServer类。下面是代码:
I have a practice project which I need help with. It's a simple MailServer class. Here's the code:
import java.util.ArrayList;
import java.util.List;
import java.util.Iterator;
import java.util.HashMap;
import java.util.TreeMap;
import java.util.Collection;
import java.util.Map;
public class MailServer
{
private HashMap<String, ArrayList<MailItem>> items;
// mail item contains 4 strings:
// MailItem(String from, String to, String subject, String message)
public MailServer()
{
items = new HashMap<String, ArrayList<MailItem>>();
}
/**
*
*/
public void printMessagesSortedByRecipient()
{
TreeMap sortedItems = new TreeMap(items);
Collection c = sortedItems.values();
Iterator it = c.iterator();
while(it.hasNext()) {
// do something
}
}
}
我有一个HashMap包含一个字符串键(邮件收件人的名字),值包含该特定收件人邮件的ArrayList。
I have a HashMap which contains a String key (mail recipient's name) and the value contains an ArrayList of the mail for that particular recipient.
我需要对HashMap进行排序,并显示每个用户的姓名,电子邮件主题和消息。
I need to sort the HashMap, and display the each user's name, email subject, and message. I'm having trouble with this section.
感谢
推荐答案
您已关闭。
TreeMap sortedItems = new TreeMap(items);
// keySet returns the Map's keys, which will be sorted because it's a treemap.
for(Object s: sortedItems.keySet()) {
// Yeah, I hate this too.
String k = (String) s;
// but now we have the key to the map.
// Now you can get the MailItems. This is the part you were missing.
List<MailItem> listOfMailItems = items.get(s);
// Iterate over this list for the associated MailItems
for(MailItem mailItem: listOfMailItems) {
System.out.println(mailItem.getSomething());
}
}
例如, TreeMap sortedItems = new TreeMap(items);
可以改进。
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