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I'm working on a game written in Scala where the user has to type "BANG" as quickly as possible in order to hunt an animal.

// ...

println("When you see an animal, type BANG as quickly as possible.")
Thread.sleep(2000 + Random.nextInt(6000))

val start = System.currentTimeMillis()
println("You see an animal!")
val bang = readLine("")
val time = System.currentTimeMillis() - start

if (bang == "BANG" && time <= 1500) {
  // ...you get the point

Unfortunately, there's a bug that makes so that you can type "BANG" ahead of time and always win, because it accepts input before the readLine().

I have tried a few different ways of clearing the input. The obvious solution, putting a readLine() before val start = System.currentTimeMillis(), doesn't work because it forces the user to press enter first.

Any ideas?

Davis Sorenson
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1 Answers1

2

There's no standard way of clearing stdin with Scala's (or even Java's) API.

You can use this lower-level implementation RawConsoleInput to clear the buffer though.

It has a read method that returns the first character in the standard input, or -2 if the buffer is clear.

Because it uses "raw input mode", instead of the usual "line mode", keys like Enter, backspace, Ctrl+C will NOT be processed by the operating system, and will remain in the buffer until read is called.

//drain standard input
while(RawConsoleInput.read(wait = false) >= 0) {
}

Signature:

/**
* Reads a character from the console without echo.
*
* @param wait
*   <code>true</code> to wait until an input character is available,
*   <code>false</code> to return immediately if no character is available.
* @return
*   -2 if <code>wait</code> is <code>false</code> and no character is available.
*   -1 on EOF.
*   Otherwise an Unicode character code within the range 0 to 0xFFFF.
*/
public static int read (boolean wait) throws IOException

Note: make sure you've imported the JNA library.

dcastro
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