如何在android上更快地将文本文件读取到ArrayList [英] how to faster read text file to ArrayList on android

问题描述

我在将 txt 文件快速读取到 ArrayList 时遇到问题.如果我想读取 0.9MB 的文件，我必须等待 5 分钟.如果文件大小为 34MB(部分原因是因为 android 不接受大于 1MB 的文件)，则它完全不起作用.我认为这个过程最多应该是几秒钟.

I have a problem with fast read txt file to ArrayList. If I want read a file size 0,9MB, I must wait 5min. If files size is 34MB (partialy, because android does not accept larger than 1MB files), it's completely not working. I think that process should be max few second.

这是一个代码:

String word; 
public ArrayList<String> dictionary = new ArrayList<String>();

public void setup() 
{

  try {
      AssetManager assetManager = getAssets();
      InputStream inputf;
      inputf = assetManager.open("dict_1.txt");
      reader = new BufferedReader(new InputStreamReader(inputf));

      word = " ";      
      while(word != null)
      {
        word =  reader.readLine();

        if (word != null)
          dictionary.add(word);
      }
      if(reader.equals("null")) println("No file found");

    } catch (NullPointerException e) {
    e.printStackTrace();
    println("No file found");
    } catch (IOException e) {
    e.printStackTrace();
    }
}

我为我的英语感到抱歉.我希望一切都可以理解.

I'm sorry for my english. I hope that all is understadable.

推荐答案

您的 ArrayList 在您添加项目时不断重新分配.这会消耗大量的 CPU 时间，尤其是随着列表的增长，因为需要在内存中复制一堆指针.更好的方法是将条目数存储为字典文件的第一项，然后预先分配ArrayList:

Your ArrayList keeps getting reallocated as you're adding items. This can consume a non-trivial amount of CPU time, especially as the list grows, since a bunch of pointers need to copied around in memory. A better approach would be to store the number of entries as the first item of the dictionary file, and then pre-allocate the ArrayList:

 dictionary = new ArrayList<String>(numberOfEntries);

更高级的优化将是一种完全不依赖于 Java 集合类的数据结构.根据您的需要，这可能是一个巨大的 UTF-8 字节数组，它可以一次性读入内存(甚至可以通过内存映射文件访问).

A more advanced optimization would be a data structure that doesn't rely on a Java collection class at all. Depending on your needs, this could be a huge UTF-8 byte array that is read into memory in one swoop (or even accessed via a memory-mapped file).

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