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Load text file to memory in Java
File file = new File("wiki.txt");
FileInputStream fileInputStream = new FileInputStream(file);
FileChannel fileChannel = fileInputStream.getChannel();
MappedByteBuffer mapByteBuffer = fileChannel.map(FileChannel.MapMode.READ_ONLY, 0, file.length());
System.out.println((char)mapByteBuffer.get());

RandomAccessFile file = new RandomAccessFile("wiki.txt", "r");
FileChannel channel = file.getChannel();
MappedByteBuffer buf = channel.map(FileChannel.MapMode.READ_WRITE, 0, 1024*50);

InputStream is = new BufferedInputStream(new FileInputStream(filename));
byte[] chars = new byte[1024];
int numberOfChars = 0;
while ((numberOfChars = is.read(chars)) != -1)
{
    for (int i = 0; i < numberOfChars; ++i)
    {
        if (chars[i] == 'n' && numberOfChars - i != 1)
        {
            ++count;
        }
    }
}
count++
return count; // number of lines

BufferedReader in = new BufferedReader(new FileReader(fileName));
for (int i = 0; i < endLine; i++)
{
    String oneLine = in.readLine();
}