Java: Program produces console output, but has run time error?

[AjAlien]

Hello,

 

I am having issues figuring out why this program is experiencing a run-time error but is producing a correct console output. I've been stuck on it for almost an hour.

 

I'd appreciate the help.

 

Code:

import java.util.Scanner;
public class ModifyArray {
	// Can't modify code above this
   public static void swapArrayEnds(int[] sortArray, int numElem)
   {
      numElem = 4;
      int i = 0;
      int tmpStore = 0;
      tmpStore = sortArray[0];
      sortArray[0] = sortArray[numElem - 1];
      sortArray[numElem - 1] = tmpStore;
   }
   // Can't modify code below this
   public static void main (String [] args) {
      int numElem = 4;
      int[] sortArray = new int[numElem];
      int i = 0;
      sortArray[0] = 10;
      sortArray[1] = 20;
      sortArray[2] = 30;
      sortArray[3] = 40;
      swapArrayEnds(sortArray, numElem);
      for (i = 0; i < numElem; ++i) {
         System.out.print(sortArray[i]);
         System.out.print(" ");
      }
      System.out.println("");
      return;
   }
}

Output:

 

[79wjd]

Don't reinitialize numElem.

 

You have an array out of bounds an exception (i.e. you're accessing an index that doesn't exist).

 

(I'm assuming there are potentially other test cases)

 

Try putting in some print statements and you'll see exactly where the exception is occurring. 

[SSL]

I don't see a runtime exception when I run this code and I don't see where one would happen.

[AjAlien]

6 minutes ago, djdwosk97 said:

Don't reinitialize numElem.

 

You have an array out of bounds an exception (i.e. you're accessing an index that doesn't exist).

 

(I'm assuming there are potentially other test cases)

 

Try putting in some print statements and you'll see exactly where the exception is occurring. 

Indeed there are other test cases, the eBook which has the exercises doesn't show them though (really not a fan of this eBook). Thank you though, your answer made a lot of sense and helped a great deal!

[79wjd]

2 minutes ago, AjAlien said:

(really not a fan of this eBook).

Yeah, neither am I. ++i is stupid. 

 

The main method also has a few interesting....quirks....in the way it's written that just add to the confusion.