比较多维HashMap的键

Question

I am working on an application with a number of custom data classes. I am taking input for my application from 2 different places and want to cross-reference between the two to help ensure the data is accurate.

I have a Map.Entry<String,HashMap<String, Integer>> object called chromosome , where each value is called a marker .

I also have a custom object called IndividualList individuals which extends HashMap<Integer,Individual> where each Individual has a method Genotype getGenotype() which returns the non-static variable genotype . Genotype extends HashMap<String,String[]>

I want to look at each the key for all my marker objects and check whether each of them are present as a key in any Individual 's genotype . Every Individual has the same keys in its genotype so I only need to test for one Individual .

The problem I am facing is which Individual to test, as because it is a HashMap I cannot simply just arbitrarily choose the first element, so what I am doing at the moment is taking the values of individuals as a Collection then converting these to an ArrayList<Individual> then taking the first of these elements (which is just an arbitrary one as HashMap is unordered) to get an Individual then taking this Individual 's genotype and comparing marker.getKey() with the keys in the genotype . Like so :

for(Map.Entry<String, MarkerPosition> marker : chromosome.getValue().entrySet())
    if(!(new ArrayList<Individual>(individuals.values()).get(0)
                    .getGenotype().containsKey(marker.getKey())))
            errors.add("Marker " + marker.getKey() + " is not present in genotype");

But as you can see, this is horrid and ugly and far too complicated, so I was wondering if there is a much simpler way of achieving what I want that I am missing.

Thanks!

Answer 1

...This question is really confusingly phrased and difficult to understand, but I'm not clear on why you don't just use

 individuals.values().iterator().next()

instead of new ArrayList<Individual>(individuals.values()).get(0) .

(If you can use third-party libraries, your code would probably be significantly clearer overall if you used a Guava Table , which is a general-purpose, significantly "cleaner" replacement for a Map<K1, Map<K2, V>> . Disclosure: I contribute to Guava.)

Answer 2

Why can you not arbitrarily choose the first element of a HashMap?

individuals.entrySet().iterator().next()
individuals.values().iterator().next()

This will probably be the same entry each time. You should make sure the map is not empty to avoid an exception.