In an interview it was asked to find non- common elements between two string arrays.

Eg: String a[]={"a","b","c","d"};
String b[]={"b","c"};
O/p should be a,d

I have answered to the question that in Java Set is implemented using HashTable. The code with Set is much simpler:

String[] a = {"a","b","c","d"};
String[] b = {"b", "c"};

Set<String> set = new HashSet<>(a.length);
for(String s : a){
    set.add(s);
}
for(String s : b){
    set.remove(s);
}
return set;

now my query is that is there any other better approach to achieve this

You can shorten the code by

TreeSet set = new TreeSet(Arrays.asList(a));
set.removeAll(Arrays.asList(b));

Demo

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