How to override the toString method in a custom implementation of TreeMap?

There is an implemented TreeMap and the toString () method is overridden in it, but I would like the implementation of this method to be more adequate. How is it possible to override a method using StringBuilder for example?

 public class MyTreeMap<K extends Comparable<K>, V> implements Set<K, V> { private Node<K, V> root; private int size; public MyTreeMap() { root = null; size = 0; } @Override public boolean containsKey(K key) { if (root == null) { return false; } return root.findKey(key); } @Override public boolean containsValue(V value) { if (root == null) { return false; } return root.findValue(value); } @Override public V get(K key) { if (root == null) { return null; } return root.getValue(key); } @Override public boolean isEmpty() { return size == 0; } @Override public V put(K key, V value) { if (root == null) { root = new Node<>(key, value); size = 1; return null; } V oldValue = root.putNode(key, value); if (oldValue == null) { size += 1; } return oldValue; } @Override public V remove(K key) { if (root == null) { return null; } return root.removeNode(key); } @Override public int size() { return size; } @Override public String toString() { if (root == null) { return "No list"; } return root.toString(); } private class Node<Key extends Comparable<Key>, Value> { private Key k; private Value v; private Node<Key, Value> parent; private Node<Key, Value> left; private Node<Key, Value> right; public Node(Key k, Value v) { this.k = k; this.v = v; parent = null; left = null; right = null; } public Node(Key k, Value v, Node<Key, Value> parent) { this.k = k; this.v = v; this.parent = parent; left = null; right = null; } public boolean findKey(Key k) { if (k.compareTo(this.k) == 0) { return true; } if (left != null && k.compareTo(this.k) < 0) { return left.findKey(k); } if (right != null) { return right.findKey(k); } return false; } public boolean findValue(Value v) { if (v.equals(this.v)) { return true; } if (left != null && left.findValue(v)) { return true; } return right != null && right.findValue(v); } public Value getValue(Key k) { if (k.compareTo(this.k) == 0) { return this.v; } if (left != null && k.compareTo(this.k) < 0) { return left.getValue(k); } if (right != null) { return right.getValue(k); } return null; } public Value putNode(Key k, Value v) { if (k.compareTo(this.k) == 0) { Value oldValue = this.v; this.v = v; return oldValue; } if (k.compareTo(this.k) < 0) { if (left != null) { return left.putNode(k, v); } left = new Node<>(k, v, this); return null; } if (right != null) { return right.putNode(k, v); } right = new Node<>(k, v, this); return null; } public Value removeNode(Key k) { if (k.compareTo(this.k) == 0) { if (left == null && right == null) { if (parent == null) { removeRoot(); } else { parent.removeMe(this); } } else if (left != null && right == null) { if (parent == null) { removeRoot(left); } else { parent.removeMe(this, left); } } else if (left == null) { if (parent == null) { removeRoot(right); } else { parent.removeMe(this, right); } } else { Node<Key, Value> replacement = right.findNextNode(); replacement.setLeft(left); if (parent == null) { removeRoot(replacement); } else { parent.removeMe(this, replacement); } } return v; } if (left != null && k.compareTo(this.k) < 0) { return left.removeNode(k); } if (right != null) { return right.removeNode(k); } return null; } private void removeMe(Node<Key, Value> node) { if (node == left) { left = null; } else { right = null; } } private void removeRoot() { root = null; } private void removeMe(Node<Key, Value> node, Node<Key, Value> replacement) { if (node == left) { left = replacement; } else { right = replacement; } } @SuppressWarnings("unchecked") private void removeRoot(Node<Key, Value> replacement) { root = (MyTreeMap<K, V>.Node<K, V>) replacement; } private Node<Key, Value> findNextNode() { if (left == null) { return this; } return left.findNextNode(); } public void setLeft(Node<Key, Value> left) { this.left = left; } public String toString() { return k + "->" + v + (left != null ? " (" + left.toString() + ")" : " ()") + (right != null ? " (" + right.toString() + ")" : " ()"); } } } 

Adding items to MyTreeMap:

  MyTreeMap<Integer, String> treeMap = new MyTreeMap<>(); treeMap.put(15, "England"); treeMap.put(12, "Poland"); treeMap.put(18, "USA"); treeMap.put(45, "Ukraine"); treeMap.put(1, "Germany"); treeMap.put(78, "Russia"); treeMap.put(3, "Sweden"); treeMap.put(80, "Italy"); treeMap.put(27, "Brazil"); treeMap.put(90, "Turkey"); 

Output to console:

 15->England (12->Poland (1->Germany () (3->Sweden () ())) ()) (18->USA () (45->Ukraine (27->Brazil () ()) (78->Russia () (80->Italy () (90->Turkey () ()))))) 

It prompted me, but I think this is not the best solution ((