Java Scanner: stop reading after the first entry

Question

Im looking for a form to make Scanner to stop reading when you push the first time (so, if I press the key K automatically the program considerer that I press the Intro key, so it stop to recognise inputs, save the K and keep going with the program).

Im using char key= sc.next().charAt(0); in a beginning, but dont know how to make it stop without pushing Intro

Thanks in advance!

what do you mean by push? are you just trying to read in 1 line from the user? — Gordon Allocman, Mar 28 '16 at 15:27
Not yet... For now Im working in other parts, dont want to stop in one thing because I cant find a solution — Frikilangelo, Apr 07 '16 at 06:42

score 1 · Answer 1 · answered Mar 28 '16 at 15:50

If you want to stop accepting after a single particular character you should read the user's input character by character. Try scanning based on a Pattern of one single character or using the Console class.

Scanner scanner = new Scanner(System.in);
Pattern oneChar = new Pattern(".{1}");
// make sure DOTALL is true so you capture the Enter key
String input = scanner.next(oneChar);
StringBuilder allChars = new StringBuilder();

// while input is not the Enter key {
    if (input.equals("K")) {
        // break out of here
    } else {
        // add the char to allChars and wait for the next char
    }
    input = scanner.next(oneChar);
}
// the Enter key or "K" was pressed - process 'allChars'

Pattern is new to me, I will take a look to it, looks like im missing something because the **new Pattern(".{1}");** part is asking me for another int argument — Frikilangelo, Mar 29 '16 at 07:03

score 0 · Answer 2 · edited May 23 '17 at 12:15

Unfortunately, Java doesn't support non blocking console and hence, you can't read user's input character by character (read this SO answer for more details).

However, what you can do is, you can ask the user to enter the whole line and process each character of it until Intro is encountered, below is an example:

System.out.println("Enter the input");
Scanner scanner = new Scanner(System.in);
String input = scanner.nextLine();
StringBuilder processedChars = new StringBuilder();
for(int i=0 ; i<input.length() ; i++){
    char c = input.charAt(i);
    if(c == 'K' || c == 'k'){
        break;
    }else{
        processedChars.append(c);
    }
}
System.out.println(processedChars.toString());

Is sad to hear that; what I wanted is the same you do there, but automatically to avoid the "extra key push". Perhaps someday we can have that option — Frikilangelo, Mar 29 '16 at 06:52

Java Scanner: stop reading after the first entry

2 Answers2

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