Question

I have never seen a comparator created inside of a constructor for a TreeMap structure. How would one go about doing this? Is there a way to make the TreeMap() constructor call the other TreeMap constructor which has a comparator argument to set up the comparator?

private Comparator<? super K> cmp;
private Node root;
private int size;
private final String indentStr = "   ";

public TreeMap() {
    // Create cmp assuming K implements Comparator
    //???  TreeMap(new Comparator<V>());
}

public TreeMap(Comparator<? super K> cmp) {
    this.cmp = cmp;
}

Answer 1

They usually set that fields to null, rather than instantiating something.

But if you want to, you can have:

this(new Comparator<K>() {
   public int compare(K k1, K k2) {
       return ((Comparable<K>) k1).compareTo(k2);
   }
});

The problem is that ClassCastException can occur, because you don’t know the type of the elements.