Infinite While loop

Question

The while loop should compare the ibsn's of these two objects. Objects being compared:

  list[0] = new ReadingMatter ("Words and Stuff", "9-082-1090-1");
  list[1] = new Magazine ("Fashion", "318921019", "Mike Dales");
  list[2] = new Book ("Rocks and Minerals", "3-323-0691-2", "Jamie Dawson");
  String[] mainCharacters = {"Lennie","George","Candy"};
  list[3] = new Novel ( "Of Mice and Men", "4-569-2190-1", "John Steinbeck", mainCharacters);
  list[4] = new TextBook ("Java, Java, Java", "3-131-9871-0", "John Smith", true);

the changed compareTo:

public int compareTo(Object other)
{
    ReadingMatter temp = (ReadingMatter)other;
    int result = 0;

    if (this.isbn.compareTo(temp.getIsbn()) > 0)
        result = -1;
    else if (this.isbn.compareTo(temp.getIsbn()) < 0)
        result = 1;

    return result;
}

the while loop

while(testing)
  {
     testing = false;

     for(int j = 0; j < list.length - 1; j++)
     {
        if (list[j].compareTo(list[j+1]) > 0)
          {
           temp = list[0];
           list[0] = list[1];
           list[1] = temp;

           testing = true;   
          }
     }
  }

is it something to do with the hyphenated numbers? how would i get around the hyphens?

EDIT: The problem is that the loop is infinite, the if statement is always being used

You haven't included enough detail for a satisfactory answer. What's the problem you're having? Where is the code for the isbn.compareTo method? Do Magazine and Book extend ReadingMatter? — Max Wallace
– Max Wallace, Commented Mar 1, 2014 at 21:33
You should parameterize your Comparable; what is more it can be rewritten as return other.isbn.compareTo(isbn); — fge
– fge, Commented Mar 1, 2014 at 21:33
I'm not sure what your problem/question is but your if/for is wrong: when j is the last valid index you compare the last item with the next one which doesn't exist. — ingenious
– ingenious, Commented Mar 1, 2014 at 21:33
yeah they extend it. oh you basically answered it. I forgot to build the isbn.compare thank you! — Johny
– Johny, Commented Mar 1, 2014 at 21:36

wumpz · Accepted Answer · 2014-03-01 21:35:35Z

1

The problem is that you always switching index 0 and 1 but checking index j and j+1:

if (list[j].compareTo(list[j+1]) > 0)
{
    temp = list[0];
    list[0] = list[1];
    list[1] = temp;

    testing = true;   
}

Therefore if you have one indexpair j, j+1 with j>2 to which compareTo delivers >0 you get your infinite loop.

answered Mar 1, 2014 at 21:35

wumpz

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3 Comments

Johny Over a year ago

i have 5 in the array, i just edited them out from simplicity

ingenious Over a year ago

and you're still always swapping list[0] with list[1]. All the other elements in the list never even get sorted, so testing is always true at the end of the loop. That's your answer.

wumpz Over a year ago

Sorry. I am still not allowed to edit this answer. I tried to print beneath a corrected version. The upper version is to point out his problems.

Jan Nielsen · Accepted Answer · 2014-03-01 21:48:38Z

0

Since your conditional only orders elements 0 and 1, you will end up with list[0] < list[1] < list[2] which sets testing=true and loops, again.

answered Mar 1, 2014 at 21:48

Jan Nielsen

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