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：

public List<Feed> loadSubscribedFeeds(File feedsFile) throws FileNotFoundException {
    Scanner s = new Scanner(feedsFile);

    List<String> listString = new ArrayList<>();
    List<Feed> listFeed = new ArrayList<>();

    while (s.hasNextLine()) {
        listString.add(s.nextLine());
    }

    for (int i = 0; i < listString.size(); i++) {
        // 这里是你需要处理的部分
        // 将 listString 中的值转换为 Feed 对象并添加到 listFeed 中
    }

    return listFeed;
}

以下是 Feed 类：

public class Feed implements Serializable, Comparable<Feed> {
    // 类的定义...

    // 其他方法和成员...
}

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

public List&lt;Feed&gt; loadSubscribedFeeds(File feedsFile) throws FileNotFoundException {
	
	Scanner s = new Scanner(feedsFile);
	
	List&lt;String&gt; listString = new ArrayList&lt;&gt;();
	List&lt;Feed&gt; listFeed = new ArrayList&lt;&gt;();
	
	while (s.hasNextLine()) {
		listString.add(s.nextLine());
	}
	
	for(int i = 0; i &lt; listString.size(); i++) {
		for(int j = 0; j &lt; listFeed.size(); j++) {
			
		}
	}
	
	return listFeed;
}

Here's the Feed class:

public class Feed implements Serializable, Comparable&lt;Feed&gt; {

    private static final long serialVersionUID = 1L;

    private String url;
    private String title;
    private String description;
    private String publishedDateString;
    private List&lt;Entry&gt; entries;

    public Feed(String url) {
        super();
        this.url = url;
        this.entries = new ArrayList&lt;Entry&gt;();
        this.title = &quot;&quot;;
        this.description = &quot;&quot;;
        this.publishedDateString = &quot;&quot;;
    }

    /**
     * Creates an instance of a Feed and transfers the feed
     * data form a SyndFeed object to the new instance.
     *
     * @param url        The URL string of this feed
     * @param sourceFeed The SyndFeed object holding the data for this feed instance
     */
    public Feed(String url, SyndFeed sourceFeed) {
        this(url);
        setTitle(sourceFeed.getTitle());
        setDescription(sourceFeed.getDescription());
        if (sourceFeed.getPublishedDate() != null)
            setPublishedDateString(FeaderUtils.DATE_FORMAT.format(sourceFeed.getPublishedDate()));
        for (SyndEntry entryTemp : sourceFeed.getEntries()) {
            Entry entry = new Entry(entryTemp.getTitle());
            entry.setContent(entryTemp.getDescription().getValue());
            entry.setLinkUrl(entryTemp.getLink());
            entry.setParentFeedTitle(getTitle());
            if (entryTemp.getPublishedDate() != null) {
                entry.setPublishedDateString(FeaderUtils.DATE_FORMAT.format(entryTemp.getPublishedDate()));
            }
            addEntry(entry);
        }
    }

    public String getUrl() {
        return url;
    }

    public void setTitle(String title) {
        this.title = title != null ? title : &quot;&quot;;
    }

    public String getTitle() {
        return title;
    }

    public void setDescription(String description) {
        this.description = description != null ? description : &quot;&quot;;
    }

    public String getDescription() {
        return description;
    }

    public void setPublishedDateString(String publishedDateString) {
        this.publishedDateString = publishedDateString != null ? publishedDateString : &quot;&quot;;
    }

    public String getPublishedDateString() {
        return publishedDateString;
    }

    /**
     * Returns a short string containing a combination of meta data for this feed
     *
     * @return info string
     */
    public String getShortFeedInfo() {
        return getTitle() + &quot; [&quot; +
                getEntriesCount() + &quot; entries]: &quot; +
                getDescription() +
                (getPublishedDateString() != null &amp;&amp; getPublishedDateString().length() &gt; 0
                        ? &quot; (updated &quot; + getPublishedDateString() + &quot;)&quot;
                        : &quot;&quot;);
    }

    public void addEntry(Entry entry) {
        if (entry != null) entries.add(entry);
    }

    public List&lt;Entry&gt; getEntries() {
        return entries;
    }

    public int getEntriesCount() {
        return entries.size();
    }

    @Override
    public boolean equals(Object obj) {
        return (obj instanceof Feed)
                &amp;&amp; ((Feed) obj).getUrl().equals(url);
    }

    @Override
    public int hashCode() {
        return url.hashCode();
    }

    @Override
    public String toString() {
        return getTitle();
    }

    @Override
    public int compareTo(Feed o) {
        return getPublishedDateString().compareTo(o.getPublishedDateString());
    }
}

答案1

得分: 1

最简单的方法是更改您的循环。

for (int i = 0; i < listString.size(); i++) {
    listFeed.add(new Feed(listString.get(i)));
}

这样，您就会向listFeed中添加一个新的Feed对象。

另一种方法是使用流API。

List<Feed> feeds = listString.stream().map(Feed::new).collect(Collectors.toList());

不过，您原来的循环技巧也是可以的。

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.

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

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

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

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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