为什么初始化这个字节数组1024 [英] why initialize this byte array to 1024

问题描述

我是比较新的Java和我试图写一个简单的Andr​​oid应用程序。我有一个在我的应用程序的文件夹资产约3500行的大的文本文件，我需要读入一个字符串。我发现如何做到这一点的好例子，但我有一个关于为什么字节数组初始化为1024。难道我想将它初始化到我的文本文件的长度问题？此外，也不会我想用字符，不是字节？这里是code：

 私人无效populateArray（）{
    AssetManager assetManager = getAssets（）;
    的InputStream的InputStream = NULL;
    尝试 {
        的InputStream = assetManager.open（3500LineTextFile.txt）;
    }赶上（IOException异常E）{
        Log.e（IOException异常populateArray，e.getMessage（））;
    }
    字符串s = readTextFile（InputStream的）;
    //添加更多code这里来填充从字符串数组
}

私人字符串readTextFile（InputStream中的InputStream）{
    ByteArrayOutputStream的OutputStream =新ByteArrayOutputStream（）;
    inputStream.length
    中byte buf [] =新的字节[1024];
    INT LEN;
    尝试 {
        而（（LEN = inputStream.read（BUF））！=  -  1）{
            outputStream.write（BUF，0，的len）;
        }
        outputStream.close（）;
        inputStream.close（）;
    }赶上（IOException异常E）{
        Log.e（IOException异常readTextFile，e.getMessage（））;
    }
    返回outputStream.toString（）;
}
 

编辑：根据你的建议，我尝试这种方法。是不是更好吗？谢谢你。

 私人无效populateArray（）{
    AssetManager assetManager = getAssets（）;
    的InputStream的InputStream = NULL;
    读者iStreamReader = NULL;
    尝试 {
        的InputStream = assetManager.open（LIST.TXT）;
        iStreamReader =新的InputStreamReader（InputStream中，UTF-8）;
    }赶上（IOException异常E）{
        Log.e（IOException异常populateArray，e.getMessage（））;
    }
    字符串字符串= readTextFile（iStreamReader）;
    //更多code在这里
}

私人字符串readTextFile（InputStreamReader的InputStreamReader的）{
    StringBuilder的SB =新的StringBuilder（）;
    烧焦BUF [] =新的char [2048];
    INT读取;
    尝试 {
        做 {
            读= inputStreamReader.read（BUF，0，buf.length）;
            如果（读＆GT; 0）{
                sb.append（BUF，0，读）;
            }
        }而（读＆GT; = 0）;
    }赶上（IOException异常E）{
        Log.e（IOException异常readTextFile，e.getMessage（））;
    }
    返回sb.toString（）;
}
 

解决方案

这个例子是不好的。这是十足的不良做法（隐藏例外，不关闭流在finally块，不指定显式编码等）。它采用的是1024字节长缓冲器，因为它没有任何办法知道输入流的长度的

阅读的Java IO教程了解如何从阅读的文本文件。

I'm relatively new to Java and I'm attempting to write a simple android app. I have a large text file with about 3500 lines in the assets folder of my applications and I need to read it into a string. I found a good example about how to do this but I have a question about why the byte array is initialized to 1024. Wouldn't I want to initialize it to the length of my text file? Also, wouldn't I want to use char, not byte? Here is the code:

private void populateArray(){
    AssetManager assetManager = getAssets();
    InputStream inputStream = null;
    try {
        inputStream = assetManager.open("3500LineTextFile.txt");
    } catch (IOException e) {
        Log.e("IOException populateArray", e.getMessage());
    }
    String s = readTextFile(inputStream);
    // Add more code here to populate array from string
}

private String readTextFile(InputStream inputStream) {
    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    inputStream.length
    byte buf[] = new byte[1024];
    int len;
    try {
        while ((len = inputStream.read(buf)) != -1) {
            outputStream.write(buf, 0, len);
        }
        outputStream.close();
        inputStream.close();
    } catch (IOException e) {
        Log.e("IOException readTextFile", e.getMessage());
    }
    return outputStream.toString();
}

EDIT: Based on your suggestions, I tried this approach. Is it any better? Thanks.

private void populateArray(){
    AssetManager assetManager = getAssets();
    InputStream inputStream = null;
    Reader iStreamReader = null;
    try {
        inputStream = assetManager.open("List.txt");
        iStreamReader = new InputStreamReader(inputStream, "UTF-8");
    } catch (IOException e) {
        Log.e("IOException populateArray", e.getMessage());
    }
    String String = readTextFile(iStreamReader);
    // more code here
}

private String readTextFile(InputStreamReader inputStreamReader) {
    StringBuilder sb = new StringBuilder();
    char buf[] = new char[2048];
    int read;
    try {
        do {
            read = inputStreamReader.read(buf, 0, buf.length);
            if (read>0) {
                sb.append(buf, 0, read);
            }
        } while (read>=0);
    } catch (IOException e) {
        Log.e("IOException readTextFile", e.getMessage());
    }
    return sb.toString();
}

解决方案

This example is not good at all. It's full of bad practices (hiding exceptions, not closing streams in finally blocks, not specify an explicit encoding, etc.). It uses a 1024 bytes long buffer because it doesn't have any way of knowing the length of the input stream.

Read the Java IO tutorial to learn how to read text from a file.

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