如何将ArrayList中的字符串值存储到一个ArrayList的对象中。
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英文:

How to store String values from an ArrayList<String> to an ArrayList<Object> of Objects

问题

我试图获取 listString 的值并将它们保存到对象列表 listFeed 中，然后返回 listFeed。到目前为止，我使用了 Scanner 从 feedsFile 中添加数据到我的 ArrayList listString，但我不知道如何将这些值存储在一个对象的 ArrayList 中。

以下是代码片段：

  1. public List<Feed> loadSubscribedFeeds(File feedsFile) throws FileNotFoundException {
  2.     Scanner s = new Scanner(feedsFile);
  4.     List<String> listString = new ArrayList<>();
  5.     List<Feed> listFeed = new ArrayList<>();
  7.     while (s.hasNextLine()) {
  8.         listString.add(s.nextLine());
  9.     }
  11.     for (int i = 0; i < listString.size(); i++) {
  12.         // 这里是你需要处理的部分
  13.         // 将 listString 中的值转换为 Feed 对象并添加到 listFeed 中
  14.     }
  16.     return listFeed;
  17. }

以下是 Feed 类：

  1. public class Feed implements Serializable, Comparable<Feed> {
  2.     // 类的定义...
  4.     // 其他方法和成员...
  5. }

在上述代码的第二个 for 循环中，你需要将 listString 中的每个值转换为 Feed 对象，并添加到 listFeed 中。你可以使用 Feed 类的构造函数来创建新的 Feed 对象，并设置相应的属性值。

以上是你需要的翻译内容。

英文:

I'm trying to get the values of listString and save them to the list of objects listFeed and return listFeed. So far I used a Scanner to add date from feedsFile to my ArrayList listString but I don't know how to store those values in an ArrayList of Objects.

Here's the code snippet

  1. public List&lt;Feed&gt; loadSubscribedFeeds(File feedsFile) throws FileNotFoundException {
  2. 	
  3. 	Scanner s = new Scanner(feedsFile);
  4. 	
  5. 	List&lt;String&gt; listString = new ArrayList&lt;&gt;();
  6. 	List&lt;Feed&gt; listFeed = new ArrayList&lt;&gt;();
  7. 	
  8. 	while (s.hasNextLine()) {
  9. 		listString.add(s.nextLine());
  10. 	}
  11. 	
  12. 	for(int i = 0; i &lt; listString.size(); i++) {
  13. 		for(int j = 0; j &lt; listFeed.size(); j++) {
  14. 			
  15. 		}
  16. 	}
  17. 	
  18. 	return listFeed;
  19. }

Here's the Feed class:

  1. public class Feed implements Serializable, Comparable&lt;Feed&gt; {
  3.     private static final long serialVersionUID = 1L;
  5.     private String url;
  6.     private String title;
  7.     private String description;
  8.     private String publishedDateString;
  9.     private List&lt;Entry&gt; entries;
  11.     public Feed(String url) {
  12.         super();
  13.         this.url = url;
  14.         this.entries = new ArrayList&lt;Entry&gt;();
  15.         this.title = &quot;&quot;;
  16.         this.description = &quot;&quot;;
  17.         this.publishedDateString = &quot;&quot;;
  18.     }
  20.     /**
  21.      * Creates an instance of a Feed and transfers the feed
  22.      * data form a SyndFeed object to the new instance.
  23.      *
  24.      * @param url        The URL string of this feed
  25.      * @param sourceFeed The SyndFeed object holding the data for this feed instance
  26.      */
  27.     public Feed(String url, SyndFeed sourceFeed) {
  28.         this(url);
  29.         setTitle(sourceFeed.getTitle());
  30.         setDescription(sourceFeed.getDescription());
  31.         if (sourceFeed.getPublishedDate() != null)
  32.             setPublishedDateString(FeaderUtils.DATE_FORMAT.format(sourceFeed.getPublishedDate()));
  33.         for (SyndEntry entryTemp : sourceFeed.getEntries()) {
  34.             Entry entry = new Entry(entryTemp.getTitle());
  35.             entry.setContent(entryTemp.getDescription().getValue());
  36.             entry.setLinkUrl(entryTemp.getLink());
  37.             entry.setParentFeedTitle(getTitle());
  38.             if (entryTemp.getPublishedDate() != null) {
  39.                 entry.setPublishedDateString(FeaderUtils.DATE_FORMAT.format(entryTemp.getPublishedDate()));
  40.             }
  41.             addEntry(entry);
  42.         }
  43.     }
  45.     public String getUrl() {
  46.         return url;
  47.     }
  49.     public void setTitle(String title) {
  50.         this.title = title != null ? title : &quot;&quot;;
  51.     }
  53.     public String getTitle() {
  54.         return title;
  55.     }
  57.     public void setDescription(String description) {
  58.         this.description = description != null ? description : &quot;&quot;;
  59.     }
  61.     public String getDescription() {
  62.         return description;
  63.     }
  65.     public void setPublishedDateString(String publishedDateString) {
  66.         this.publishedDateString = publishedDateString != null ? publishedDateString : &quot;&quot;;
  67.     }
  69.     public String getPublishedDateString() {
  70.         return publishedDateString;
  71.     }
  73.     /**
  74.      * Returns a short string containing a combination of meta data for this feed
  75.      *
  76.      * @return info string
  77.      */
  78.     public String getShortFeedInfo() {
  79.         return getTitle() + &quot; [&quot; +
  80.                 getEntriesCount() + &quot; entries]: &quot; +
  81.                 getDescription() +
  82.                 (getPublishedDateString() != null &amp;&amp; getPublishedDateString().length() &gt; 0
  83.                         ? &quot; (updated &quot; + getPublishedDateString() + &quot;)&quot;
  84.                         : &quot;&quot;);
  85.     }
  87.     public void addEntry(Entry entry) {
  88.         if (entry != null) entries.add(entry);
  89.     }
  91.     public List&lt;Entry&gt; getEntries() {
  92.         return entries;
  93.     }
  95.     public int getEntriesCount() {
  96.         return entries.size();
  97.     }
  99.     @Override
  100.     public boolean equals(Object obj) {
  101.         return (obj instanceof Feed)
  102.                 &amp;&amp; ((Feed) obj).getUrl().equals(url);
  103.     }
  105.     @Override
  106.     public int hashCode() {
  107.         return url.hashCode();
  108.     }
  110.     @Override
  111.     public String toString() {
  112.         return getTitle();
  113.     }
  115.     @Override
  116.     public int compareTo(Feed o) {
  117.         return getPublishedDateString().compareTo(o.getPublishedDateString());
  118.     }
  119. }

答案1

得分: 1

  1. 最简单的方法是更改您的循环。
  3. for (int i = 0; i < listString.size(); i++) {
  4.     listFeed.add(new Feed(listString.get(i)));
  5. }
  7. 这样，您就会向listFeed中添加一个新的Feed对象。
  9. 另一种方法是使用流API。
  11. List<Feed> feeds = listString.stream().map(Feed::new).collect(Collectors.toList());
  13. 不过，您原来的循环技巧也是可以的。
  15. 一个小提示，您不需要显式调用`super()`，如果您没有使用不同版本的super，它会被自动调用。
英文:

The simplest way is to change your loop.

  1. for(int i = 0; i &lt; listString.size(); i++) {
  2.     listFeed.add( new Feed( listString.get(i) );
  3. }

That way you're adding a new Feed object to the listFeed.

Another way you could do it is to use the stream api.

  1. List&lt;Feed&gt; feeds = listString.stream().map( Feed::new ).collect( Collectors.toList() );

Your original technique with a loop is fine though.

A minor note, you do not need to call super() explicitly it will be called automatically if you don't use a different version of super.

huangapple
  • 本文由 发表于 2020年9月3日 16:31:10
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  • arraylist
  • java
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