java - 用Java从文件中获取值

Question

如何从文本文件 myFile.txt 中获取与 i 相对应的值(如果 i=5，我必须获取 57.05698808926067)？该值可能会持续到 25000。

0->37.6715587270802
1->40.02056806304368
2->351.65161070935005
3->54.74486689415533
4->86.12063488461266
5->57.05698808926067
6->0.0
7->56.078343612293374

Answer 1

使用此代码:

// Note: bounds checking left as an exercise
public double getDoubleFromFile(final String filename, final int index)
    throws IOException
{
    final List<String> list = Files.readAllLines(paths.get(filename),
        StandardCharsets.UTF_8);

    return Double.parseDouble(list.get(index));
}

但是，这会占用整个文件。如果您必须查询多次，为什么不呢？另一种解决方案:

public double getDoubleFromFile(final String filename, final int index)
    throws IOException
{
    final Path path = Paths.get(filename);
    int i = 0;
    String line;
    try (
        final BufferedReader reader = Files.newBufferedReader(path,
            StandardCharsets.UTF_8);
    ) {
        while ((line = reader.readLine()) != null) {
            if (index == i)
                return Double.parseDouble(line);
            i++;
        }
        return Double.NaN;
    }
}