TreeSet giving incorrect output - Java8

Question

While working with a tree set, I found very peculiar behavior.

As per my understanding following program should print two identical lines:

public class T         


        

Answer 1

To add some information about why the remove of TreeSet actually removes case-insensively in your example (and provided that you follow the if (size() > c.size()) path as explained in the answer by @Shadov) :

This is the removemethod in TreeSet :

public boolean remove(Object o) {
        return m.remove(o)==PRESENT;
    }

it calls remove from its internal TreeMap :

public V remove(Object key) {
    Entry p = getEntry(key);
    if (p == null)
        return null;

    V oldValue = p.value;
    deleteEntry(p);
    return oldValue;
}

which calls getEntry

 final Entry getEntry(Object key) {
        // Offload comparator-based version for sake of performance
        if (comparator != null)
            return getEntryUsingComparator(key);
        if (key == null)
            throw new NullPointerException();
        @SuppressWarnings("unchecked")
            Comparable k = (Comparable) key;
        Entry p = root;
        while (p != null) {
            int cmp = k.compareTo(p.key);
            if (cmp < 0)
                p = p.left;
            else if (cmp > 0)
                p = p.right;
            else
                return p;
        }
        return null;
    }

If there is a Comparator (as in your example), the entry is searched based on this Comparator (this is done by getEntryUsingComparator), that's why it is actually found (then removed) , despite the case difference.