What does System.in.read actually return?

问题

What does :

System.in.read()

return ? The documentation says :

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

But for example if I enter : 10 I get back 49 . Why is that ?

回答1:

49 is the ASCII value of the char 1. It is the value of the first byte.

The stream of bytes that is produced when you enter 10Enter on your console or terminal contains the three bytes {49,48,10} (on my Mac, may end with 10,12 or 12 instead of 10, depending on your System).

So the output of the simple snippet

int b = System.in.read();
while (b != -1) {
    System.out.println(b);
    b = System.in.read();
}

after entering a 10 and hitting enter, is (on my machine)

49
48
10

回答2:

System.in.read() reads just one byte.

49 is the Unicode point value for 1.

Try to print:

System.out.println((char)49);

This will help you to understand it more.

回答3:

When you enter 10, it is not read as an integer but as a String or, more precisely here, an array of bytes.

49 is the ASCII code for the character 1.

来源：https://stackoverflow.com/questions/15273449/what-does-system-in-read-actually-return