String operations hang on android?

Question

I'm writing an android app that requires that I retrieve the html code of a webpage and get and return specific elements. For some reason, the code seems to hang or take an unbelievably long time doing basic string operations.

    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;

Takes minutes to complete on both the emulator and the device with university connection speeds. Whereas

    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++;

takes ~ 5 seconds and returns the correct number of lines in the html page. Why do the string operations take so long? Just for perspective, the page is about 4000 lines long.

score 2 · Accepted Answer · edited May 23 '17 at 12:15

Because you're doing it wrong. Use StringBuilder to build large Strings.

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.

String operations hang on android?

1 Answers1