Java's TreeSet implementation of contains (Sourcecode) missing

Question

When I open the sourcecode of the TreeSet Class there is the following code:

public boolean contains(Object o) {
    return m.containsKey(o);
}

m is a NavigableMap which is an interface. So where is the implementation? It is definitely not in TreeSet itself.

Answer 1

From the source for TreeSet:

TreeSet(NavigableMap<E,Object> m) {
    this.m = m;
}

public TreeSet() {
    this(new TreeMap<E,Object>());
}

So m should be a TreeMap (or possibly another implementation of NavigableMap if another class in the same package calls that constructor).