Java Map data structure that recognizes order of Integers stored as Strings

Question

I have the following data:

"1" --> "Label 1"
"2" --> "Label 2"
"11" --> "Label 11"
"22" --> "Label 22"

which I would like to store in a map that would enforce order of integers, instead of lexicographic order. Is there any *Map that Java already has for this purpose?

Use a TreeMap and provide your own Comparator that orders by integer value. — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Nov 13, 2014 at 17:05

Louis Wasserman · Accepted Answer · 2014-11-13 17:27:31Z

2

Use TreeMap with custom Comparator.

Like:

    TreeMap<String, String> map = new TreeMap<>(new Comparator<String>() {
        @Override
        public int compare(String o1, String o2) {
            return Integer.compare(Integer.parseInt(o1), Integer.parseInt(o2));
        }
    });

The keys will be ordered according to passed Comparator.

Above is just example, but based on your usecase you may change implementation of compare() to reflect your business need.

edited Nov 13, 2014 at 17:27

Louis Wasserman

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answered Nov 13, 2014 at 17:08

brb tea

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4 Comments

chiastic-security Over a year ago

This doesn't work if the values get really big and can be negative, because the difference can overflow.

brb tea Over a year ago

@chiastic-security if values too big, then it will not overflow, but will throw Exception. As OP has only informed about Integer type, and it is solution of that.

chiastic-security Over a year ago

No, I don't mean too big to be parsed. I mean that each one is a valid Integer, but the difference is bigger than Integer.MAX_VALUE. That won't throw an exception, it'll just give wrong answers (which is worse).

brb tea Over a year ago

@chiastic-security I updated my answer. And thanks for suggesting integer overflow.

chiastic-security · Accepted Answer · 2014-11-13 17:26:48Z

Yes, you can use a TreeMap or a ConcurrentSkipListMap, each of which implements SortedMap, and allows you to provide a Comparator at map creation time.

Either implement it as going from Integer as the key, or leave it as a String but supply a comparator that works by converting to Integer and using that for comparison.

I'd have thought it would be cleaner to use Integer as the key, but it won't make much difference.

If you go down the String route, do it like this. It's the same as Huko's code, but doesn't go wrong with large negative values where the difference might cause an overflow.

TreeMap<String, String> map = new TreeMap<>(new Comparator<String>() {
    @Override
    public int compare(String o1, String o2) {
        return Integer.parseInt(o1).compareTo(Integer.parseInt(o2));
    }
});

EDIT: Huko's code now takes this into account too.

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