Bubblesort Issue within Method

[burrish]

Hello, again. I'm getting an exception message when trying to pass strings to this method:

import java.util.Scanner;

public class Search {

	public static void main(String[] args) {
	
		Scanner sc = new Scanner(System.in);
		Scanner bc = new Scanner(System.in);
		String[] firstName = new String[25];
		String[] lastName = new String[25];
		int nameCount = 0;
		
		System.out.print("How many names would you like to enter? ");
		nameCount = bc.nextInt();
		System.out.print("\n");
		
		for (int i = 0; i < nameCount; i++) {
			System.out.println("Enter first name: ");
			firstName[i] = sc.nextLine();
		}
		sortName(nameCount, firstName);
	
	
	}
	public static void sortName(int nCount, String[] fName) {
		String tmpStr;
		for (int i = 0; i < nCount; i++) {
			if (fName[i].compareTo(fName[i + 1]) > 0) {
				tmpStr = fName[i];
				fName[i] = fName[i + 1];
				fName[i + 1] = tmpStr;
				}
			}
		for (int i = 0; i < nCount; i++)
			System.out.println(fName[i]);
		}
	
	
	}

Exception in thread "main" java.lang.NullPointerException
	at java.lang.String.compareTo(String.java:1167)
	at Search.sortName(Search.java:28)
	at Search.main(Search.java:21)

I'm simply trying to arrange these first names into alphabetical order. I also tried to add ".length - 1" to the end of "nCount", but it says a delimiter isn't allowed. All help is appreciated!

[JosAH]

Hello, again. I'm getting an exception message when trying to pass strings to this method:

And now we have to guess what Exception has been thrown at you and at which line?

kind regards,

Jos

[burrish]

....apologies. The exception has been added.

[Norm]

Since your posted code does not have 28 lines, can you tell
Which variable on line 28 is null? If you can't tell by looking, add a println call to print out the values of all the variables on that line.

add ".length - 1" to the end of "nCount", but it says a delimiter isn't allowed. All help is appreciated!

nCount is a primitive NOT an object reference. There are no attributes for a primitive.
You could use .length with fName.

[doWhile]

Look at how you are accessing the array in the loop where the exception is thrown (assuming the line numbers line up between your exception and code). For example, what happens when i is equal to nCount-1? Has the object at the array position nCount-1+1 been instantiated? Also note your algorithm will not fully sort the array.

[burrish]

Thanks to all of you for the replies, so far. I appreciate the clarification, Norm.

No, it doesn't look like nCount-1+1 has been instantiated for use, so I'm going to adjust the numbers to try and make it work. I've seen that most bubblesort algorithms use two for-loops, but I didn't think it was necessary in my method since I'm comparing rows of single strings.

[burrish]

Guys, I'm about to pull my hair with these "NullPointer" exceptions. For simplicity's sake, I decided to forgo bubblesort and use the Array class to do a really short test-program to test the sorting functionality. Here's the code:

import java.util.Scanner;
import java.util.Arrays;

public class Sorter {

	public static void main(String[] args) {
		
			Scanner sc = new Scanner(System.in);
			String[] firstName = new String[25];
			// String[] firstName = {"Brandon", "Kim", "Aaron", "Larry", "Gary"};
			
			System.out.println("Enter five names: ");
			
			for (int i = 0; i < 5; i++) {
				firstName[i] = sc.nextLine();
				}
				
			Arrays.sort(firstName);
			
			for (int i = 0; i < 5; i++) 
 				System.out.println(firstName[i]);
			
			
			
	}



}

If you run this code and enter the five names, it throws out the following exception:

Exception in thread "main" java.lang.NullPointerException
	at java.lang.String.compareTo(String.java:1167)
	at java.lang.String.compareTo(String.java:92)
	at java.util.Arrays.mergeSort(Arrays.java:1144)
	at java.util.Arrays.mergeSort(Arrays.java:1155)
	at java.util.Arrays.mergeSort(Arrays.java:1155)
	at java.util.Arrays.sort(Arrays.java:1079)
	at Sorter.main(Sorter.java:18)

If you comment out the prompt for names, the for-loop that scans the names, and then you uncomment the initialized array, the sort method works exactly as it should. What in the HECK am I doing wrong??

[Norm]

The array has 25 slots and you are putting data in 5 of them.
What does the sort() method do with slots with null values?

[burrish]

What does the sort() method do with slots with null values?

It throws out an exception because there's nothing there. :) Thanks!

I guess I was expecting it to dynamically adjust to however many names the user decides to enter as long as I had a long enough array.

[Norm]

Go back to the API doc and see if there are other overrides for sort that will do what you want.