system.in.read 未命中执行 [英] system.in.read miss execution

问题描述

为什么在第一个循环之后，switch 会执行两次，然后才会停下来等待我的输入?标准输入中是否有任何字符?我该如何解决这个问题?

Why after the first loop, the switch will execute twice before it stop to wait for my input? Is there any char left in the standard input? How can I fix the issue?

while(true)
{
int choice = System.in.read();
switch(choice)
{
   case '1':
       break;
   default:
       break;
}
}

推荐答案

InputStream#read 只读取单个 byte 并且不会消耗换行符(将是 2 个字符，LF和 CR 在 Windows 平台上)，将其传递到下一个 read.此 read 现在将不阻塞接收到的输入，并且流程将落入您的 default 案例.

InputStream#read only reads a single byte and will not consume the newline character (will be 2 characters, LF and CR on Windows platforms), passing it through to the next read. This read will now not block having received input and the flow will fall through to your default case.

您可以使用 BufferedReader 代替并阅读整行:

You could use a BufferedReader instead and read a full line:

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
...
int choice = Integer.parseInt(br.readLine());

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