Java IO：为什么从stdin读取时，换行符的数字表示出现在控制台上？

Question

Just for getting a better understanding of what I've heard in a lecture (about Java Input- and Output-Stream) I've made myself this tiny program:

public static void main (String[] args) throws Exception {
    int input;
    FileOutputStream fos = new FileOutputStream("test.txt");

    // 95 is the underscore-char ( _ ). I use it
    //  for to finish it reception of input.
    while ((input = System.in.read()) != 95) {
        fos.write(input);
        out.println(input);
    }

    out.println("- Finished -");

    fos.close();
}

It prints the numerical representation of the character I've just typed to stdout. It works basically but here is what I see in Eclipse:

"10" is the decimal ASCII representation of the line feed.

Okay. I've pressed the enter-key for to finish the iteration.

But why does this second value appear too?

I would expect only the first key (the actual character) to appear.

If somehow can explain the issue then I would appreciate his / her answer.

@Sanket Makani Here's the corresponding content of the text-file "text.txt":

2
3
A
a

In Eclipse:

Answer 1

InputStreams can be used for binary formats, binary formats don't care about filtering new line characters.

You will either need to filter them yourself, or use a buffered reader/scanner and read line, then iterate along the characters in the string.

https://docs.oracle.com/javase/7/docs/api/java/io/InputStream.html#read()

Shows that it indeed does only read one character at a time, however the eclipse terminal may not be forwarding the data entered until you press enter.

When that happens your loop is running twice.

Scanner docs: https://docs.oracle.com/javase/8/docs/api/java/util/Scanner.html#nextLine--

Answer 2

As you said so yourself, its treating the newline as part of your input as well.

Please refer to this question on SO, it might be helpful to what you wish to accomplish.

How to read integer value from the standard input in Java

Answer 3

The newline is part of your input stream, so System.in.read() sees it as well. If you only want to print the character codes of characters within the line, you need to filter out the line feed characters.