How can I create and infinite loop and exit it with a command?

Question

I was wondering if I could make it so a loop can end with typing in a command like end or -1. What I have now is

while ( gradeCounter <= 10 ) // loop 10 times

I would like to know how to have it loop infinitely till I end it.

Use a boolean variable in the conditional statement and set it to false when you want to break out of the loop. — toniedzwiedz, Oct 01 '13 at 19:46
Make the condition to be false and it will break. If you want it to be a console input you can research on `Scanner` usage and compare the String/input to break the condition. — porfiriopartida, Oct 01 '13 at 19:47
Hi, I am like very new to java and I am not sure how to use boolean — Joyal, Oct 01 '13 at 19:47
@porfiriopartida that depends on the condition :) You're right. Comment fixed. — toniedzwiedz, Oct 01 '13 at 19:48
@Cube This is exactly the same: `boolean condition = true; while ( condition ) { condition = gradeCounter <= 10; }` — porfiriopartida, Oct 01 '13 at 19:48

score 2 · Accepted Answer · edited Jun 20 '20 at 09:12

2

Simply create a while loop and a condition to break it

while(true){
      String inputString = //Get user input here       

      if(inputString.equals("Your Termination Text"))
           break;

    }

If you want to know how to get console input here is one method Java: How to get input from System.console()

Edit per comments below

double grades = 0;
int entries = 0;
while(true){
      String inputString = //Get user input here       
 
      if(inputString.equals("Your Termination Text"))
           break;
      else{
        grades += Double.parseDouble(inputString);
        entries++;
      }
 }
 double averageGrade = grades / entries;

Please keep in mind that this does not account for text that is not a number and also not your termination text. From the question it sounds like a low level CIS class and I don't think this will be an issue. If it is however you need to learn how to do try catch and some more input validation.

edited Jun 20 '20 at 09:12

Community

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answered Oct 01 '13 at 19:48

DotNetRussell

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It's worth mention that the same thing can be done with all of the loops. Put the above loop body into `for(;;){//loop body from above}` or `do{//loop body from above}while(true);` Just a matter of personal preference. – nhgrif Oct 01 '13 at 19:50
If I have average = total / 10 How do I do average for infinite loop? – Joyal Oct 01 '13 at 19:51
1

If you need to average, the `for` loop is actually pretty good method. `for(int i=0;;i++){//find sum, divide by i}` – nhgrif Oct 01 '13 at 19:52
You can also use a less clean but just as effective counter declared outside of your loop then just increment it each iteration with counter++ – DotNetRussell Oct 01 '13 at 19:53
@AMR i have, in the end to take the average of all data entered. How do I do that if I changed it from set 10 to infinite? – Joyal Oct 01 '13 at 19:54
@Cube I hate to state the obvious but if your loop is infinite it never ends. How do you get the average of something that never ends? – DotNetRussell Oct 01 '13 at 19:55
@AMR When I do use a command like end can I take the average of where it ended? – Joyal Oct 01 '13 at 19:57
@Cube Also please tell me what you are attempting to average? – DotNetRussell Oct 01 '13 at 19:57
@AMR Yea, I have to make a Gradebook data entry thing for homework and in the end it should take average of all the data entered. So If I enter 3 in the end it should give me the average of the 3 if I enter 500 then the average of 500. Thanks for your time – Joyal Oct 01 '13 at 20:00
@Cube that should be your solution above – DotNetRussell Oct 01 '13 at 20:04
1

@SamYonnou That concept is probably a bit to advanced for someone who would even post this original question... – nhgrif Oct 01 '13 at 20:08
@AMR Thank you so much for your help. If it doesn't work can I reply back? – Joyal Oct 01 '13 at 20:12
@Cube I have given you the tools and the resources to do this project. There is a time when you need to do some research yourself. This is a pretty basic CIS problem. If you want to succeed in future classes you need to learn to get friendly with Java Documentation. Good luck bud – DotNetRussell Oct 01 '13 at 20:13
@AMR Thanks, sorry I just wasn't sure how to average an infninite loop – Joyal Oct 01 '13 at 20:27
@Cube if this answers your question please make sure to select the check mark so future people know which answer works – DotNetRussell Oct 01 '13 at 21:47

score 1 · Answer 2 · answered Oct 01 '13 at 19:50

While(true) {} creates an infinite loop. A break command inside the loop breaks out of it. You'll have to detect whatever sort of event will occur inside the loop to determine if you should break.

I don't know what you're doing on a larger scale, but it could be a better idea to use Threads which don't loop infinitely and suck up processing power.

ppeterka · Answer 3 · 2013-10-01T20:06:08.673

Yes, it is possible. Just make sure, there is a different thread that can handle some kind of input...

public class MyBreakableInfiniteLoop

    public static void main(String[] args) {

        MyRunnable r = new MyRunnable();
        new Thread(r).start();

        System.out.println("Press Enter to stop thread");
        new Scanner(System.in).readLine();
        r.stop = true;

    }

    public static class MyRunnable extends Runnable {
       public volatile boolean stop = false;
       public void run() { 
           while(!stop) { 
              //do nothing, preferably in a meaningful way 
           } 
       }
    }


}

(aLso, I didn't take into count kill -9 as "input that breaks the infinite loop"...)

How can I create and infinite loop and exit it with a command?

3 Answers3

Edit per comments below