Taking input with Scanner : need to exit on pressing enter key

[Rahul Sudip Bose]

I want to take strings from the user and stop taking input when :

1-he enters nothing and presses only enter. OR if this is not possible,
2-he enters "exit".

What is the code to be put inside the while loop below for the above cases to happen ?
I tried has next , has next line , !has next("exit") and failed. Please tell me how to proceed.

import java.util.*;

public class Input
{
	public static void main(String[ ] args)
	{
	  Scanner in = new Scanner(System.in);
	  System.out.println("Enter some strings !");
	  List<String> list = new ArrayList<String>( );

		while(????) //What to enter here ?
		{
		  list.add(in.nextLine( ));	  
		}
	  
	}//main ends

}

[Wouter Oet]

So your program needs to run forever but it needs to stop when the user either enters nothing or exit. Hint: break.

[Rahul Sudip Bose]

Here is the revised program. User can exit upon entering "pl exit".But one problem remains how to exit if he presses enter key twice, without entering anything else ?

import java.util.*;

public class Input
{
	public static void main(String[ ] args)
	{
	  Scanner in = new Scanner(System.in);
	  System.out.println("Enter some strings !");
	  List<String> list = new ArrayList<String>( );
	  boolean loop = true;
		while(loop)
		{
		  String s = in.nextLine( );

			if(s.equals("")|s.equals("pl exit"))
			{
			  break;	
			}
			else
			{
		  	  list.add(s);
			}
		}
	  
	}//main ends

}

thanks for the hint.
rb

PS : here is another problem i had long ago while using the Scanner class :
http://www.coderanch.com/t/528543/java/java/Taking-input-keyboard-takes-ints#2397967

[Campbell Ritchie]

I don't like break; myself. The idiom for that sort of thing in the heading of a while loop is not the sort of thing you can work out unless you have seen it. Try this sort of thing

while ((line = myScanner.nextLine()).length() > 0)
{
   . . . 
}

You can add a second test with the && operator, but don't call nextLine() twice.

[Rahul Sudip Bose]

Campbell Ritchie wrote:I don't like break; myself. The idiom for that sort of thing in the heading of a while loop is not the sort of thing you can work out unless you have seen it. Try this sort of thing

while ((line = myScanner.nextLine()).length() > 0)
{
   . . . 
}

You can add a second test with the && operator, but don't call nextLine() twice.

Love you man... . By the way, what is an "idiom" saw it in the sun docs too, just ignored it and there was no loss of continuity.
Here is the revised program :

import java.util.*;

public class Input
{
	public static void main(String[ ] args)
	{
	  Scanner in = new Scanner(System.in);
	  List<String> list = new ArrayList<String>( );
	  String line = null;
	  System.out.println("Enter some strings !");

		while ((line = in.nextLine( )).length( ) > 0)  
		{	
		  list.add(line);
		}
	  
	}//main ends

}

sample output :

Enter some strings !
rrr                                                  
                                                      pressed enter !

C:\rb\java progs>java Input
Enter some strings !                        
                                                      pressed enter !                                            

[Rahul Sudip Bose]

Your help has made another program possible. I use the above code in the program below :

//Replace all occurences of a String "val" in a list with "newVal" (see below)

import java.util.*;

public class Replace
{
	public static <String> void replace(List<String> list, String val, String newVal) 
	{
       for (ListIterator<String> it = list.listIterator( ); it.hasNext( ); )
		{
		  Object x = it.next( ); // using Object instead of String
        	 	  if (val == null ?  x == null : val.equals(x))
                   	  it.set(newVal);
		}
	}// the useful method ends


	public static void main(String[ ] args)
	{
	  System.out.println("You can replace all String occurences with a desired string !");
	  Scanner in = new Scanner(System.in);
	  List<String> list = new ArrayList<String>( );
	  String line = null;	
	  System.out.println("Enter some strings !");

		while ((line = in.nextLine( )).length( ) > 0)  
		{	
		  list.add(line);
		}


	 //Show the user what he entered above.

		for(ListIterator<String> it = list.listIterator( ); it.hasNext( ); )
		{
		  System.out.print(it.next( ) + " ");	
		}

	 System.out.println("\n\nNow which string in above output do you want to replace ?");
	 String val = in.nextLine( );	 
	 System.out.println("\nWhat do you want to replace it with ?");
	 String newVal = in.nextLine( );	
	 System.out.println("\nReplacing it...");
	 Replace.replace(list, val, newVal);

	 System.out.println("\nAfter replacement you get : \n");

	 for(ListIterator<String> it = list.listIterator( ); it.hasNext( ); )
		{
		  System.out.print(it.next( ) + " ");	
		}
	  
	}//main ends

}

This code works fine if you enter each sentence word by word (as shown below) :

Enter some strings !
you
are
fast
you
are
funny

But it obviously fails when the input is given as below :

Enter some strings !
you are fast
you are funny

How to resolve the above problem. Will it require major rewriting of code ?

thanks for hearing
rb

[Campbell Ritchie]

Rahul Sudip Bose wrote: . . . Will it require major rewriting of code ? . . .

Yes. You would have to change nextLine() to next()

You might have to enter ctrl-D or ctrl-Z to terminate entry if you use that technique, and use hasNext() to continue with the loop.

And an idiom is something that is said in a particular context, which would otherwise appear incorrect. It is a linguistic term. An example of an English idiom is "raining cats and dogs".