Converting Hashmap into single string array in java

I'm working on a program for class and have been beating my head for days on this. I have to find the number of occurrences in a string. I've been able to get the results into a HashMap. However, I need to be able to convert it to a single string array so that I can assertTrue and test it. Here's what I have so far. Any suggestions would be greatly appreciated. Thanks.

public static void main(String[] args) { String input = "xyz 456 123 123 123 123 123 123 xy 98 98 xy xyz abc abc 456 456 456 98 xy"; //String to be tested String[] str = input.split(" "); // String put into an array

    Map<String, Integer> occurrences = new HashMap<String, Integer>();
    Integer oldValue = 0;

    for (String value : str)
    {
        oldValue = occurrences.get(value);
        if (oldValue == null)
        {
            occurrences.put(value, 1); 
        } else
        {
            occurrences.put(value, oldValue + 1);
        }
    }
    occurrences.remove("");

}