5

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 ?

andrel
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saplingPro
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3 Answers3

13

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
Andreas Dolk
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  • Because `10` is two bytes. A byte representing the character 1, followed by a byte representing the character `0`. – Stephen C Mar 07 '13 at 14:24
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    @saplingPro The thing to realize is that when you enter "10", you're not entering the _number_ 10, but rather _text_ which happens to be "10" but could have been "foo" or even "☃ is melting!". What `System.in` sees are the bytes of this _text_ stream. For ascii and extended ascii (so, not my little snowman up there), check out http://www.ascii-code.com – yshavit Mar 07 '13 at 15:35
5

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.

Maroun
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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.

Fabien
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