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Editorial Team
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Asked: 2026-05-15T23:27:21+00:00

Why doesn’t Set.size() match the number of elements in the set’s iterator? I’m using

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Why doesn’t Set.size() match the number of elements in the set’s iterator?

I’m using a HashSet, and I added some duplicate values. Those duplicates were automatically eliminated since I used a set. Set.size() is returning 16. When I actually iterate over the elements, I get 13.

What can be causing this difference? Am I doing it right?

Set set = new HashSet();
...
System.out.println ("Found " + set.size() + " tokens...");
Iterator it = set.iterator();
int i = 0;
while (it.hasNext()) {
    i++;
    System.out.println(Integer.toString(i) + ": " + (String)it.next());
}

Here’s the output from the console:

Found 16 tokens...
1: 3 Months Free HD Extra Pack
2: Best Buy - $30 for 3 Months (Instant Rebate)
3: Gift Card - Fry's - $100 (HDTV Offer)
4: 6 Months FREE Showtime
5: 3 Months Free HD Access
6: Savings Certificate Booklet
7: 3 months FREE Showtime (rolls off month 4)
8: Free NASCAR Hotpass
9: 3 Months Free DVR Service
10: $0 Delivery & Handling
11: 1 Year Free Showtime
12: $99 Off Advance Equipment (2nd AP)
13: Best Buy - $30 for 12 Months (Instant Rebate)
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1 Answer

  1. Editorial Team

    Seriously this is not possible. HashSet is a well-established enough class that there is no possibility of a bug like you describe being in it. Here are some ways you could make this happen:

    • Screwing around with the set using Reflection like Mark Peters suggests;
    • You have caused an exception to be thrown after the 13th element which terminates the program
    • Overriding the behavior of Set to make it inconsistent
    • You are using different sets for the printout of the total and the items
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