java - FileInputStream 读取如何工作？

Question

有人请解释一下如何在以下代码中填充缓冲区数组:

try {
        byte[] buffer = new byte[1024];
        //(1) this print an empty string?
        System.out.println("1: " + new String(buffer));
        FileInputStream inputStream = new FileInputStream("test.txt");
        int len;

        while((len = inputStream.read(buffer)) != -1) {
            //(2) this print text on my file?
            System.out.println("2: " + new String(buffer));
        }
        inputStream.close();

    } catch (IOException e) {
        e.printStackTrace();
    }

更新:阅读以下内容后我得到了有用的信息: https://docs.oracle.com/javase/tutorial/essential/io/bytestreams.html

Buffered input streams read data from a memory area known as a buffer; the native input API is called only when the buffer is empty. Similarly, buffered output streams write data to a buffer, and the native output API is called only when the buffer is full

谢谢大家!

Answer 1

InputStream#read 方法会将数据从输入流读取到提供的缓冲区中。

请参阅java doc了解详情。

(特别是查看返回值 - 如果没有更多数据可供读取，它将返回 -1。)