关于Java中的for循环的困惑

Question

I wrote a for loop like this:

for(int i = 0; (char) System.in.read() != 's'; i++){
    System.out.print(i);
}

I expected the program to keep printing numbers until I type s on the keyboard. However, every time I typed a letter, I got three numbers on the command prompt:

a
012
q
345

There should be only one number printed on the console after each letter typed, but there are three. Why?

Answer 1

正如您的一些评论者所述，问题不在于for（）循环，而在于System.in.read（），该问题还将提供输入流中的回车符/换行符作为字符（这也是为什么您的输出分布在多行中，而不是所有内容都在一行中）

Answer 2

Like Brian said in the comments, it's because the input is buffered. When you type a and then hit the enter key that enter key is flushing the buffer and you are seeing the loop execute 3 times. Once for the first character, a , and twice more for the \\n and \\r characters representing the new line and carriage return characters.