Question about scanners?

[William Nerem]

Hi guys, new to java and to JavaRanch, dont' hate my silly questions, I'll have pleanty!

So about scanners, I"m having issues at the moment scanning a string like: Tom 4.56232 Blanken 1.230.

How would one skip the double numbers and just print "Tom" & "Blanken"? Thanks!

[William Nerem]

*Edit Note* Keep getting compile errors when trying to run it. I tried skipping it, with Scanner.next, but... no luck there.

[Tony Docherty]

Welcome to the Ranch.

Can you show the code you are running and the compiler errors you are getting.

[William Nerem]

Well...

public class Test2 {
	public static void main(String[] args) throws FileNotFoundException {
		File file = new File("top10.txt"); // Open the File.
		Scanner scanner = new Scanner(file);

		while (scanner.hasNextLine()) { // While more lines.
			String line = scanner.nextLine(); // Get more lines.

			Scanner lineScanner = new Scanner(line); // Create new Scanner.
			System.out.print(lineScanner.next() + " " + "\n"); // Print first

			// Scanner lineTwoScanner = new Scanner(line);
			// lineTwoScanner.next();
			// System.out.print(lineTwoScanner.next() + " " + "\n");

			while (lineScanner.hasNextInt()) {
				System.out.print(lineScanner.next() + " " + "\n");
			}

		}

		scanner.close();
	}

}

What I have marked out is the part I'm stuck on, trying to get this loop to print everything except for the names. How to get around a double variable?

Error is:

Exception in thread "main" java.util.NoSuchElementException
	at java.util.Scanner.throwFor(Unknown Source)
	at java.util.Scanner.next(Unknown Source)

Top10.txt looks like this:

1880
John 8.1541 Mary 7.2381
William 8.0511 Anna 2.6678

[William Nerem]

Shouldn't... Bob 3.4000 Richardson

System.out.print(lineScanner.next() + " ");
lineScanner.next();
System.out.print(lineScanner.next() + " ");

Print Bob Richardson? Why doesn't lineScanner.next() work in the loop with doubles?

[William Nerem]

I suppose the best approach, to avoid this NoSuchElementException is to make a hasNextDouble()... so if I have that, lets try printing the doubles...

Ok weird, it printed the year, and not the double values in the top10.txt... why'd it do that?

Scanner lineScanner = new Scanner(line); 
			
			while (lineScanner.hasNextDouble()){
				System.out.print(lineScanner.next() + " " + "\n");

Edit --- *AfterPostThoughts*:

So... 8.1456 isn't a double?

What does this mean?

// assign locale as US to recognize double numbers in a string
scanner.useLocale(Locale.US);

Anybody have any advice, I'm drowning here lol....

[Tony Docherty]

William Nerem wrote:Shouldn't... Bob 3.4000 Richardson

System.out.print(lineScanner.next() + " ");
lineScanner.next();
System.out.print(lineScanner.next() + " ");

Print Bob Richardson? Why doesn't lineScanner.next() work in the loop with doubles?

The following works for me:

    String text = "Bob 8.1541 Richardson";

    Scanner scanner = new Scanner(text);
    scanner.useLocale(Locale.US);

    System.out.print(scanner.next() + " ");
    scanner.next();
    System.out.print(scanner.next() + " ");

[Winston Gutkowski]

William Nerem wrote:Anybody have any advice, I'm drowning here lol....

Yes (and I know I'm going to get a lot of flak for it, so I will add that it's ONLY my opinion ):
Don't use Scanner's "typed" methods.

IMO, the ONLY method you need to know about with Scanner - apart from close(), which almost everyone forgets - is: nextLine().

If you type something in AND press the 'ENTER' key, you will always get a String; and furthermore, your Scanner will always be in a state to accept another "line" of input (not always the case if you don't).

What you DO with that line, after you've got it, is then entirely up to you.

I should add that the above only works if you are simply using Scanner to accept keyboard input. If you want to double it up to also accept input from a file, then you have to box a bit more clever; but it sounds like that's not your situation.

Winston

[William Nerem]

while (scanner.hasNextLine()) { // While more lines.
			String line = scanner.nextLine(); // Get more lines.

			Scanner lineScanner = new Scanner(line); 
			scanner.useLocale(Locale.US);
			
			System.out.print(lineScanner.next() + " " + "\n");
			System.out.print(lineScanner.next() + " " + "\n");

There is where my debugging stops me, it told me source not found? So it printed the first line, 1880, and it stops at Bob...

[Ramesh Pramuditha Rathnayake]

I run your first code and I didn't get any runtime exceptions.
And you don't have to use another Scanner and search line by line. The next() method of the Scanner will keep search in the next line if the current line has end.

	Scanner lineScanner = new Scanner("abcd 12.3456 efgh"); 
        System.out.println(lineScanner.nextDouble());

What do think will print here..? 12.3456.. No, here you get that runtime error. But, if there weren't that abcd answer will be 12.3456

Scanner lineScanner = new Scanner(line);
while (lineScanner.hasNextDouble()){
System.out.print(lineScanner.next() + " " + "\n");

The text on the file do not contain double value in the first place, except the first line. Therefore hasNextDouble() works only for first line.

So you have to keep searching for a double value, if find one print it. And if it is not the end of the file, keep doing that thing.

                Scanner scanner = new Scanner(file);  
		while(scanner.hasNext()){
			if (!scanner.hasNextDouble()){  
				scanner.next();
			}else{
				System.out.print(scanner.next() + " " + "\n");
			}
		}
		scanner.close(); 

Actually, your question was to print the names, not the doubles. I think this may help.

[Winston Gutkowski]

William Nerem wrote:There is where my debugging stops me, it told me source not found? So it printed the first line, 1880, and it stops at Bob...

My apologies. Didn't read the whole thread (cautionary tale to others ).

I'm still not clear where you're getting this error, because you've commented out some code and haven't included the line number (or a comment stating where you ARE getting it). nextInt() would throw something like it on line 2 of your file because it doesn't start with an integer; but you seem to be precluding that with hasNextInt() (Edit: Doh! But of course, you're not since, as Ramesh pointed out, that number is NOT an integer).

I think you need to give us ALL the details, and your code EXACTLY as you executed it.

Furthermore, your 'lineTwoScanner' field is redundant because it's based on the exact same String as 'lineScanner'.

Suggestion: Have you considered using String.split() instead? This strikes me as a VERY fiddly case for a Scanner.

Winston

[William Nerem]

I'm actually working through this problem slowly. Thanks for the input / idea's. Here's my current code with no errors:

package testing;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Locale;
import java.util.Scanner;

public class Test2 {
	public static void main(String[] args) throws FileNotFoundException {

		// Open the File.
		File file = new File("top10.txt");
		Scanner scanner = new Scanner(file);
		scanner.useLocale(Locale.US);

		// While more lines.
		while (scanner.hasNextLine()) {
			// Get the next line.
			String line = scanner.nextLine();

			// Parse the line with a temporary Scanner.
			Scanner lineScanner = new Scanner(line);
			while (lineScanner.hasNextInt()) {
				System.out.print(lineScanner.next() + " ");
			}

			while (lineScanner.hasNextLine()) {
				System.out.print(lineScanner.next() + " ");
				if (lineScanner.hasNextDouble())
					lineScanner.next();
				if (lineScanner.hasNextLine()) {
					System.out.print(lineScanner.next() + " ");
					if (lineScanner.hasNextLine()) 
						break;
					
					

				}

			}

		}

		scanner.close();
	}

}

So what I'm trying to do is print the year and first two names in this document.

1880
John 8.1541 Mary 7.2381
William 8.0511 Anna 2.6678
James 5.0057 Emma 2.0521
Charles 4.5167 Elizabeth 1.9865
George 4.3292 Minnie 1.7888
Frank 2.7380 Margaret 1.6167
Joseph 2.2229 Ida 1.5081
Thomas 2.1401 Alice 1.4487
Henry 2.0641 Bertha 1.3523
Robert 2.0404 Sarah 1.3196
1881
John 8.0975 Mary 6.9986
William 7.8712 Anna 2.7291
James 5.0253 Emma 2.0574
George 4.3068 Elizabeth 1.8733
Charles 4.2828 Margaret 1.6771
Frank 2.6170 Minnie 1.6720
Joseph 2.2679 Ida 1.4556
Henry 2.1599 Annie 1.3413
Thomas 2.1072 Bertha 1.3392
Edward 2.0103 Alice 1.3231

So I should print:
1880 John Mary
1881 John Mary

I'm not there yet because I have to find a way to break the while loop after I find the first 2 names while avoiding those stupid doubles.

[Winston Gutkowski]

William Nerem wrote:I'm not there yet because I have to find a way to break the while loop after I find the first 2 names while avoiding those stupid doubles.

Right, and this goes back to my first piece of advice: forget every method except nextLine() (and hasNextLine()).

Assuming you can rely on the format you've shown us, this would be my solution:

// Finds a line with *exactly* n space-delimited fields
// and returns them
private String[] findLine(Scanner scanner, int numFields) {
   while (scanner.hasNextLine()) {
      String[] fields = scanner.nextLine().trim().split("\\s+");
      if (fields.length == numFields)
         return fields;
   }
   return null;
}

...
// and for your loop...
while (scanner.hasNextLine()) {
   String[] fields = findLine(scanner, 1);
   if (fields == null) // didn't find a year line
      break;
   Integer year = Integer.valueOf(fields[0]);

   fields = findLine(scanner, 4);
   if (fields == null) // didn't find a names line
      break;
   String man = fields[0];
   String woman = fields[2];

   System.out.println(year + " " + man + " " + woman);
}

Do you see the logic? Instead of trying to trawl through each field individually, I just split each line up. If it has 1 field, I assume its a "year" line, and if it has 4, I assume it's a "names" line. Furthermore, if I'm looking for a year line, I can ignore any lines that don't have exactly 1 field, and conversely if I'm looking for a "name" line, I can ignore any that don't have 4.

I should add that this is only ONE way of doing it; there are many others, including solutions that use Scanner throughout. You might also need to refine it slightly if a "year" line must be followed by a name line, or there are other types of line in the file.

HIH

Winston