java的while循环错误？ 附加输出代码有什么问题？

Question

class demoWhile{        
public static void main(String args[])
    throws java.io.IOException{
        char ch = (char)System.in.read();
        while(ch!='w'){
            System.out.println("Hi"+ch);
            ch = (char)System.in.read();
        }
    }
}

-first I gave the input a 'r' and expected output was "Hir" then input option but instead received output was Hir, Hi, Hi then the input option. why it shows two additional Hi, Hi?

Answer 1

I suspect that you run this on a windows machine and pressed Enter after the 'r'. If that's not the case, ignore this answer.

The enter is understood as a linebreak, which consist of the two bytes 0D 0A on windows. In String literals these are usually expressed as "\\r\\n" .

That causes three characters to be read: 'r', '\\r' (char 13) and '\\n' (char 10).

Your code processes them individually, so the output is

Hir
Hi\r
Hi\n

But the \\r and \\n dont get displayed since they only have an effect (on windows) when you combine them.