public class WordProbability extends ProbabilityPair<Str>
{
    public WordProbability(String tag)
    {
        super(tag);
    }
    ...
}

public abstract class ProbabilityPair<T>
{
    public T key;
    private int count;
    private double probability;

    protected ProbabilityPair(T key)
    {
        this.key = key;
        count = 1;
        probability = 0d;
    }

    public void increment()
    {
        ++count;
    }
    ...
}

public class Words
{
    public List<WordProbability> words;
    public int totalCount;

    public Words()
    {
        words = new ArrayList<>();
        totalCount = 0;
    }

    public void add(WordProbability word)
    {
        if (words.contains(word))
        {
            words.get(words.indexOf(word)).increment();
        } else
        {
            words.add(word);
        }
        ++totalCount;
    }
    ...
}

public class Container<ProbabilityPair>
{
    private List<ProbabilityPair> members;
    private int totalCount;

    public void add(ProbabilityPair member)
    {
        if (members.contains(member))
        {
            members.get(members.indexOf(member)).increment();
        } else
        {
            members.add(member);
        }
        ++totalCount;
    }
}