为什么输入与“-1”相比？

Question

我在 I/O 上复习示例代码时看到一些让我感到困惑的东西：

public class CopyBytes {
public static void main(String[] args) throws IOException {

    FileInputStream in = null;
    FileOutputStream out = null;

    try {
        in = new FileInputStream("xanadu.txt");
        out = new FileOutputStream("outagain.txt");
        int c;

        while ((c = in.read()) != -1) {
            out.write(c);
        }

如何将一个 int 值 (c) 分配给输入流 (in.read()) 中的一个字节数据？为什么while循环等待它不等于-1？

Answer 1

这个 (c = in.read()) 将 return -1 当输入结束时 while 循环将停止。

阅读这篇很棒的文章 answer。

来自 Oracle 文档：

public abstract int read() throws IOException Reads the next byte of data from the input stream. The value byte is returned as an int in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value -1 is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown. A subclass must provide an implementation of this method.

Returns: the next byte of data, or -1 if the end of the stream is reached. Throws: IOException - if an I/O error occurs.

Answer 2

来自 FileInputStream.read() 的文档：

public int read() throws IOException

因此 read() returns 是整数，而不是字节，因此可以将其分配给 int 变量。请注意，int 可以隐式转换为 int 而不会丢失。同样来自文档：

Returns: the next byte of data, or -1 if the end of the file is reached.

针对-1 的循环检查确定是否已到达文件末尾，如果是则停止循环。

为什么输入与“-1”相比？

Why is an input compared with "-1"?

java

file-io

primitive-types