如何使用DataInputStream实现阅读器类

Question

我想学习如何实现一个阅读器类，只实现所需的方法来读取某些数据类型的输入。我在geeksforgeeks上看到了下面的代码，但我真的不明白buffersize或bytes或datainputstream等的用法。我想知道是否有人可以帮助分解代码，或指出我在正确的方向，所以一些相关的资源?

// Working program using Reader Class
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Scanner;
import java.util.StringTokenizer;
public class Main {
static class Reader {
final private int BUFFER_SIZE = 1 << 16;
private DataInputStream din;
private byte[] buffer;
private int bufferPointer, bytesRead;

public Reader()
{
din = new DataInputStream(System.in);
buffer = new byte[BUFFER_SIZE];
bufferPointer = bytesRead = 0;
}

public Reader(String file_name) throws IOException
{
din = new DataInputStream(
new FileInputStream(file_name));
buffer = new byte[BUFFER_SIZE];
bufferPointer = bytesRead = 0;
}

public String readLine() throws IOException
{
byte[] buf = new byte[64]; // line length
int cnt = 0, c;
while ((c = read()) != -1) {
if (c == 'n') {
if (cnt != 0) {
break;
}
else {
continue;
}
}
buf[cnt++] = (byte)c;
}
return new String(buf, 0, cnt);
}

public int nextInt() throws IOException
{
int ret = 0;
byte c = read();
while (c <= ' ') {
c = read();
}
boolean neg = (c == '-');
if (neg)
c = read();
do {
ret = ret * 10 + c - '0';
} while ((c = read()) >= '0' && c <= '9');

if (neg)
return -ret;
return ret;
}

public long nextLong() throws IOException
{
long ret = 0;
byte c = read();
while (c <= ' ')
c = read();
boolean neg = (c == '-');
if (neg)
c = read();
do {
ret = ret * 10 + c - '0';
} while ((c = read()) >= '0' && c <= '9');
if (neg)
return -ret;
return ret;
}

public double nextDouble() throws IOException
{
double ret = 0, div = 1;
byte c = read();
while (c <= ' ')
c = read();
boolean neg = (c == '-');
if (neg)
c = read();

do {
ret = ret * 10 + c - '0';
} while ((c = read()) >= '0' && c <= '9');

if (c == '.') {
while ((c = read()) >= '0' && c <= '9') {
ret += (c - '0') / (div *= 10);
}
}

if (neg)
return -ret;
return ret;
}

private void fillBuffer() throws IOException
{
bytesRead = din.read(buffer, bufferPointer = 0,
BUFFER_SIZE);
if (bytesRead == -1)
buffer[0] = -1;
}

private byte read() throws IOException
{
if (bufferPointer == bytesRead)
fillBuffer();
return buffer[bufferPointer++];
}

public void close() throws IOException
{
if (din == null)
return;
din.close();
}
}

public static void main(String[] args)
throws IOException
{
Reader s = new Reader();
int n = s.nextInt();
int k = s.nextInt();
int count = 0;
while (n-- > 0) {
int x = s.nextInt();
if (x % k == 0)
count++;
}
System.out.println(count);
}
}

Answer 1

这段代码没有多大意义:DataInputStream是用来读取二进制数据的。这里，只使用读取一个字节的read方法，并且一个简单的InputStream可以做到这一点。

Answer 2

InputStream有一个函数read，它将字节转换为缓冲区，然后您需要转换为原语，我们使用buffered read，因为直接文件访问很慢。此外，它建议您使用java.nio.file与BufferedReader，它执行许多其他方便的工具与方法，如readLine()。Nio代表新io。