Scanner

[Ankur kothari]

why doesnt this run?

 import java.util.Scanner;
public class Scanner1
{
	public static void main(String args[])
	{
		String s1="";
		 Scanner s=new Scanner(System.in);//Scanner s=new Scanner(args[0]); this runs? what is the difference?
	 s.useDelimiter("d");
		while(s.hasNext())
		{
			s1+=s.next();
		}
		System.out.println(s1);
}
}   

WHAT DOES THIS MEAN? Scanner s=new Scanner(System.in) ....i want to scan what the use has entered....i can use the console method readline here..

[Ankur kothari]

if i removed while and simply used used s.next() i get the answer.....but why does the while method go on and on?

[rohan yadav]

I am not sure abt your problem, but i think problem is in System.in argument which is passed to Scanner constructor.
I run the same program using the String as argument to constructor it works fine, same goes for command line arguments

I have done following modification

 import java.util.Scanner;
public class Scanner1
{
	public static void main(String args[])
	{
		String s1="";
		Scanner s=new Scanner("Rohan 2Yadav2 rwr");//Scanner s=new Scanner(args[0]); this runs? what is the difference?
		
		
	 s.useDelimiter("\\d");
		while(s.hasNext())
		{
			s1+=s.next();
			//System.out.println(s1);
		}
		System.out.println(s1);
}
}      

And i got output as
Rohan Yadav rwr

[Devaka Cooray]

From the documentation

Scanner.hasNext() Returns true if this scanner has another token in its input. This method may block while waiting for input to scan.

Since you specified System.in as the input source for the scanner, the hasNext test returns 'true' unless the input stream is closed. There are no usage of using the hasNext() method here with System.in as the hasNext() doesn't know whether the user *will* input something further or not. In other words, each invocation of next() method requires a lookup on the specified input (here System.in) that causes the user to input something again.