scanner.hasNext() results in an infinite loop

问题

I have a piece of code which should read input word by word and add the length of the word to an ArrayList recursively (for a school exercise).

I wrote this method:

ArrayList<Integer> wordLengths = new ArrayList<Integer>();
Scanner scanner = new Scanner(System.in);
// ...
private void readWords() {
    // read a word, if there are more words, read the next word
    this.wordLengths.add(this.scanner.next().length());

    if (this.scanner.hasNext()) {
        readWords();
    }
}

When I call this method, it keeps asking for new words. It won't stop the (recursive) loop. Why is this happening? this.scanner.hasNext() should only be true when there's a next word in the input so it should stop when there is no other word.

回答1:

System.in is an input stream. It is never closed, so it will always return true for #hasNext()

回答2:

Use Ctrl+Z(+Enter) in Windows or Ctrl+D in Unix to send EOF and terminate input stream

来源：https://stackoverflow.com/questions/19101776/scanner-hasnext-results-in-an-infinite-loop