Building a binary tree with a node sharing the same information

I wanted to build a binary tree in java where some nodes should be the same as in the other part.

For example, I have a tree on one side and a node on the other side (Set class). On the other side of the node is the node which will also be in the tree. And that a node in the tree can be multiple or single.

So basically, we have a node communicating with a tree. When I change the content of this node, it should also change the content in the tree! So I decided to write something as a proof of concept and couldn't do it ...

This is my code: Main class

public class Main {

    public static void main(String [] args) {
        Set s = new Set();
        System.out.println(s.toString());

        Node n1 = new Node(new String("2"),null,null);
        Node n2 = new Node(new String("3"),null,null);
        Node n3 = new Node(new String("+"),n1,n2);

        s.setIdentifier(n3);
        System.out.println(s.toString());
    }
}

      

        
        
        
      

    

Install class

public class Set {
    private Node identifier; // This is the node where is apart of the tree
    private Node head; // This is the head of the tree

    // Pre-Condição : Cria o conjunto de universo
    public Set() {
        Node id = new Node(new String("x"), null, null);
        this.identifier = id;
        Node left = new Node(new String("<"), this.identifier, new Node(new String("0"), null, null));
        Node right = new Node(new String(">="), this.identifier, new Node(new String("0"), null, null));
        this.head = new Node(new String("&&"), left, right);
    }

    // Pre-Condicao : Cria o conjunto vazio
    public Set(String identifier) {
        Node id = new Node(identifier);
        this.identifier = id;
        this.head = null;
    }

    // Pre-Condicao: Cria o conjunto dado
    public Set(String identifier, Node h) {
        Node id = new Node(identifier);
        this.identifier = id;
        this.head = h;
    }

    public Node getHead() {
        return head;
    }

    public void setHead(Node head) {
        this.head = head;
    }

    public void setIdentifier(Node identifier) {
        if (this.identifier != null) {
            this.identifier = identifier;
        }
    }

    public Node getIdentifier() {
        return this.identifier;
    }

    public void isntASet() {
        this.identifier = null;
    }

    public String toStringSort(String type) {
        StringBuilder s = new StringBuilder();
        if (this.identifier != null && this.head != null) {
            s.append(this.identifier.toStringSort(type));
            s.append(" | ");
            s.append(this.head.toStringSort(type));
        }
        return s.toString();
    }

    public String toString() {
        StringBuilder s = new StringBuilder();
        if (this.identifier != null && this.head != null) {
            s.append(this.toStringSort("infix"));
        } else if (this.identifier != null && this.head == null) {
            s.append("{");
            s.append(this.identifier.toStringSort("infix"));
            s.append(" | ");
            s.append(" }");
        } else {
            s.append("Problem detected with the expression of the Set (not a boolean Expression).");
        }
        return s.toString();
    }
}

      

        
        
        
      

    

Node Class

public class Node {
    private String data;
    private Node left;
    private Node right;

    public Node(String data) {
        this.data = data;
        this.left = null;
        this.right = null;
    }

    public Node(String data, Node left, Node right) {
        this.data = data;
        this.left = left;
        this.right = right;
    }

    public Node(Node n) {
        this.data = n.getData();
        this.left = n.getLeft();
        this.right = n.getRight();
    }

    public String getData() {
        return data;
    }

    public void setData(String data) {
        this.data = data;
    }

    public Node getLeft() {
        return left;
    }

    public void setLeft(Node left) {
        this.left = left;
    }

    public Node getRight() {
        return right;
    }

    public boolean doesLeft() {
        return (this.left != null) ? true : false;
    }

    public boolean doesRight() {
        return (this.right != null) ? true : false;
    }

    public void setRight(Node right) {
        this.right = right;
    }

    public Node clone() {
        return new Node(this);
    }

    public String toStringSort(String type) {
        StringBuilder s = new StringBuilder();

        if (type.equals("prefix")) {
            s.append(this.data.toString());
            if (this.left != null) {
                s.append(this.left.toStringSort("prefix"));
            }
            if (this.right != null) {
                s.append(this.right.toStringSort("prefix"));
            }
        } else if (type.equals("infix")) {
            if (this.left != null) {
                s.append("(" + this.left.toStringSort("infix"));
            }
            s.append(this.data.toString() + " ");
            if (this.right != null) {
                s.append(this.right.toStringSort("infix") + ")");
            }
        } else if (type.equals("postfix")) {
            if (this.left != null) {
                s.append(this.left.toStringSort("postfix"));
            }
            if (this.right != null) {
                s.append(this.right.toStringSort("postfix"));
            }
            s.append(this.data.toString());
        }
        return s.toString();
    }

    public String toString() {
        StringBuilder s = new StringBuilder();

        s.append(this.data.toString());

        return s.toString();
    }
}

      

        
        
        
      

    

And the result of my output from my main class is as follows:

x  | ((x < 0 )&& (x >= 0 ))
(2 + 3 ) | ((x < 0 )&& (x >= 0 ))

      

        
        
        
      

    

Usually every "x" that appears in my function should be replaced with "2 + 3". Which is not replaced as shown in the picture ... What's wrong with my code? Should I be using a different architecture? Thank.