Java Scanner hasNextInt（）导致无限循环

Question

What I am trying to do is have the user enter a lot of numbers and then hit enter, and then store all those numbers onto a stack at once. My thought was to use a loop to go through all the numbers and push them onto the stack like so:

Stack<Integer> mainBin = new Stack<Integer>();

Scanner scanner = new Scanner(System.in);

while (scanner.hasNextInt()) {          
mainBin.push(scanner.nextInt());
}

However, even after I press enter many times without entering anything new, it still stays in the loop. Any suggestions?

Answer 1

Scanner.hasNextInt() skips over whitespace to find the next token. So it reads and skips over all your Enter presses. Then it waits for more input, because there may be more input coming.

In a Linux terminal, you can press Ctrl-D (maybe Cmd-D on OS X?) to send an end-of-file marker, which tells the application that there is no more input coming (this should be done at the start of a line). This answer suggests that Ctrl-Z is the equivalent in Windows' command prompt.

Alternatively, you could have some special input that your application reads. @phatfingers commented that you could specify the number of values to read as the very first input. You could also have a special value to signify the end (0 or -1 are common choices, based on the application's needs), or maybe even use a non-numeric token like "end".

Answer 2

Your example uses scanner.hasNext() . Use scanner.hasNextInt() instead.