comparing keys of two hashmaps

[Mohit Sinha]

Hi All,

I want to identify the identical keys amongst two haspmaps (H1 and H2).
Also I need to identify elements of H1 not available in H2 and vice versa.

Currently I am using the HashMap interface containsKey method but have to do something like this

- loop throught all keys of H1 and H2.containsKey(h1_key)
- loop throught all keys of H2 and H1.containsKey(h2_key)

Ist there a better view to implement the same.


Thanks

[Pat Farrell]

If you use the Google Collections package, it has functions to do the usual intersection, union, and difference functions for sets.

[Vivek K Singh]

You do not need to loop thru both the maps, you can do something like:

	for (Map.Entry<String, String> me : hashmap1.entrySet()) // assuming your map is Map<String, String>
		if(hashmap2.containsKey(me.getKey()))
			System.out.println("Found Duplicate -> " + me.getKey());

This will get all keys from the hashmap1 and compare to the hashmap2 and print duplicates...

[Rob Spoor]

Or use keySet() in combination with the bulk operators:

// union
Set<String> union = new HashSet<String>(h1.keySet());
union.addAll(h2.keySet());

// h1 - h2
Set<String> diff1 = new HashSet<String>(h1.keySet());
diff1.removeAll(h2.keySet());

// h2 - h1
Set<String> diff2 = new HashSet<String>(h2.keySet());
diff1.removeAll(h1.keySet());

// intersection
Set<String> intersect = new HashSet<String>(h1.keySet());
intersect.retainAll(h2.keySet());