Inserting scanner input directly into arraylist

Question

I wanted to extract input from my scanner and insert it directly into a typesafe arraylist. Here is my code:

public static void main(String args[])
{
    List<Integer> arglist=new ArrayList<Integer>();
    List<Integer> resultlist=new ArrayList<Integer>();
    Scanner in=new Scanner(System.in);
    System.out.println("Scanning");
    while(in.hasNext())
    {
        arglist.add(in.nextInt());
    }
    System.out.println("Scan complete, sorting...");
    System.out.println(arglist);
    resultlist=qksort(arglist);
    System.out.println(resultlist);

}

This works only when I explicitly terminate input using Ctrl+Z. Shouldn't the stream terminate when I press "Enter"?

No with System.in. It will work with a file as input, but with System.in you will only have the EOF flag set when you hit Ctrl + Z. Your while body will run any time you press Enter, for every word in the line, but the hasNext method will wait for the OS return again, so, unless you terminate the console input, it will wait forever. — Jean Jung
– Jean Jung, Commented Sep 22, 2015 at 10:41

sprinter · Accepted Answer · 2015-09-22 11:27:58Z

1

No it won't terminate when you press the enter key. The scanner will read that as a newline character and interpret it as a delimiter between tokens and happily continue.

A very simple solution if you want to continue processing is:

while (in.hasNextInt()) {
    argList.add(in.nextInt());
}

That way the first time you type something that isn't a number or whitespace (e.g. "exit") it will continue.

If you particularly want to just input a single line then you can use the scanner to read a line and then scan that line:

Scanner scanner = new Scanner(System.in);
scanner = new Scanner(scanner.nextLine());

edited Sep 22, 2015 at 11:27

answered Sep 22, 2015 at 11:16

sprinter

28.1k8 gold badges51 silver badges81 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Tom Over a year ago

"The scanner will read that as a newline character and happily continue." To be more precise ... it ignores the newline character. Like hasNextInt.

sprinter Over a year ago

@Tom it will still consider it a delimiter for the purpose of defining a token right? I'm not sure what you mean by ignoring it - isn't it treated like any other whitespace?

sprinter Over a year ago

@Tom I realised it was a bit ambiguous so tried to make it clearer in my answer.

Tom Over a year ago

Yes, that is better. next() doesn't care about whitespace and doesn't read them. It waits for valid tokens. nextLine() on the other hand handles new line characters.

Manoj · Accepted Answer · 2015-09-22 10:49:14Z

0

If End of Stream didn't appear as in case of Files or 'Ctrl + Z' in case of standard input, then hasNext() method is blocking...it means-
Either it finds pattern in buffer: in this case it return True.
Or if it goes for reading from underline stream: in this case it might block.

edited Sep 22, 2015 at 10:49

answered Sep 22, 2015 at 10:44

Manoj

766 bronze badges

Collectives™ on Stack Overflow

Inserting scanner input directly into arraylist

2 Answers 2

4 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related