What structure is underlying Java TreeSet?

Question

Java TreeSet is a red-black tree self balancing structure.

But what is the structure to store the data? Array or linked list?

It's a red-black tree. It's not an array, it's not a linked list, it's a tree. — Louis Wasserman, Sep 19 '18 at 16:55
You just answered your own question. It's a [red-black tree](https://en.wikipedia.org/wiki/Red%E2%80%93black_tree). — David Conrad, Sep 19 '18 at 16:55
have you guys ever heard how trees are stored at memory? I mean linked nodes or nodes at array? — arminvanbuuren, Sep 19 '18 at 19:23

score 2 · Accepted Answer · answered Sep 19 '18 at 17:16

TreeSet is backed by a TreeMap (in similar way HashSet is backed by HashMap). If you look at TreeSet constructor:

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

TreeMap internally stores data using nodes represented with TreeMap.Entry class:

static final class Entry<K,V> implements Map.Entry<K,V> {
    K key;
    V value;
    Entry<K,V> left;
    Entry<K,V> right;
    Entry<K,V> parent;
    boolean color = BLACK;
...

There is no additional array or list there.

So nodes are linked to each other by references – arminvanbuuren Sep 19 '18 at 19:24 — arminvanbuuren, Sep 19 '18 at 19:24

What structure is underlying Java TreeSet?

1 Answers1