java - 字符串操作在android上挂起？

Question

我正在编写一个 Android 应用程序，它要求我检索网页的 html 代码并获取并返回特定元素。由于某种原因，代码似乎挂起或花费令人难以置信的长时间来执行基本字符串操作。

    URL url = new URL(link);
    URLConnection urlConnection = url.openConnection();
    InputStreamReader i = new InputStreamReader(
            urlConnection.getInputStream());
    BufferedReader in = new BufferedReader(i);
    String check = "";
    String html = "";
    while((check = in.readLine()) != null)
        html += check;

在模拟器和具有大学连接速度的设备上只需几分钟即可完成。鉴于

    URL url = new URL(link);
    URLConnection urlConnection = url.openConnection();
    InputStreamReader i = new InputStreamReader(
            urlConnection.getInputStream());
    BufferedReader in = new BufferedReader(i);
    String check = "";
    String html = "";
    int p = 0;
    while((check = in.readLine()) != null)
        p++;

大约需要 5 秒并返回 html 页面中正确的行数。为什么字符串操作需要这么长时间？仅出于透视目的，该页面大约有 4000 行长。

Answer 1

因为你做错了。使用StringBuilder构建大型字符串。

StringBuilder sb = new StringBuilder();
while((check = in.readLine()) != null)
    sb.append(check);
html = sb.toString();

Why StringBuilder when there is String?

String does not allow appending. Each method you invoke on a String creates a new object and returns it. This is because String is immutable - it cannot change its internal state.