convert Object[] from a hashmap keyset to String[]?

Question

Set<String> keys = mappings.keySet();
String[] keyArray = (String[]) keys.toArray();

String hashmapDetails = "";
for(int p=0; p < keyArray.length; p++){
    String[] details = keyArray[p].split("/");
    hashmapDetails += details[1];
    hashmapDetails += mappings.get(keyArray[p]);
    if (p != keyArray.length -1){
        hashmapDetails += ";";
    }
}

Pardon my lack of understanding but I'm trying to explore the usage of hashmaps. I understand that the toArray() returns an Object[]. However, is it not possible to type cast it to a String[]? As you can see in the codes, later, I need to go through an array and do some splitting and other String manipulation.

By doing this I got an error:

java.lang.ClassCastException: java.lang.Object[] cannot be cast to java.lang.String[]

Any guidance on how I should tackle this is greatly appreciated. Thanks!

Answer 1

You can't simply cast an Object[] array to a String[] array. You should instead use the generic version of toArray, which should work better:

String[] keyArray = keys.toArray(new String[keys.size()]);

Also note that you could simply iterate over the entrySet (that will save all the get calls) and use a StringBuilder for better string concatenation efficiency:

StringBuilder hashmapDetails = new StringBuilder();
for(Map.Entry<String, String> e : mappings.entrySet()) {
    String[] details = e.getKey().split("/");
    hashmapDetails += details[1];
    hashmapDetails += e.getValue();
    hashmapDetails += ";";
}

String result = hashmapDetails.substring(0, hashmapDetails.length() - 1);

Answer 2

It is possible to cast keyset to String[]. Try this:

String[] keys = map.keySet().toArray(new String[0]);