How to solve problem with binary tree print

Question

I did a code that take as input integers, for example: 123 11 200 1 100 150 2000 and need to output a binary tree, in this form:

      ┌1
   ┌11┤
   │  └100
123┤
   │   ┌150
   └200┤
       └2000

but in my code output is:

0┐
 │      ┌1 
 │   ┌11┤
 │   │  └100 
 └123┤
     │   ┌150 
     └200┤
         └2000

At he root appear a zero and I do not know why. This is my code. I consider that the problem is in the add() method, but do not know how to solve it. I will be grateful for help.

    public class TreeNode extends BinaryTree implements PrintableTree {
    private int i;
    private TreeNode leftChild;
    private TreeNode rightChild;

    public TreeNode(int i) {
        this.i = i;
    }

    public TreeNode() {

    }

    @Override
    public void add(int i) {
        if (i > this.i) {
            if (this.rightChild == null) {
                this.rightChild = new TreeNode(i);
            } else {
                this.rightChild.add(i);
            }
        } else {
            if (this.leftChild == null) {
                this.leftChild = new TreeNode(i);
            } else {
                this.leftChild.add(i);
            }
        }
    }

    public int getI() {
        return i;
    }

    public void setLeftChild(TreeNode leftChild) {
        this.leftChild = leftChild;
    }

    public void setRightChild(TreeNode rightChild) {
        this.rightChild = rightChild;
    }

    public TreeNode getLeftChild() {
        return leftChild;
    }

    public TreeNode getRightChild() {
        return rightChild;
    }



    @Override
    public String prettyPrint() {

        StringBuilderPlus builder = new StringBuilderPlus();
        prettyPrint(builder, "", "", "", "");

        return builder.toString();
    }

   public void print() {
       StringBuilderPlus res = new StringBuilderPlus();
       prettyPrint(res, "", "", "", "");
    }

    public void prettyPrint(StringBuilderPlus result, String prefix, String left, String mid, String right) {
        String indent = " ".repeat(String.valueOf(i).length());
        if (leftChild != null) {
            leftChild.prettyPrint(result, prefix + left + indent, " ", "┌", "│");
        }
        result.appendLine(prefix + mid + i
                + " ┐┘┤".charAt((leftChild != null ? 2 : 0)
                + (rightChild != null ? 1 : 0)));
        if (rightChild != null) {
            rightChild.prettyPrint(result, prefix + right + indent, "│", "└", " ");
        }
    }
}
public class StringBuilderPlus {

    private StringBuilder sb;

    public StringBuilderPlus(){
        sb = new StringBuilder();
    }

    public void append(String str)
    {
        sb.append(str != null ? str : "");
    }

    public void appendLine(String str)
    {
        sb.append(str != null ? str : "").append(System.getProperty("line.separator"));
    }

    public String toString()
    {
        return sb.toString();
    }
}
class BinaryTree {
    private TreeNode root;

    public void Print() {
        if (root != null) {
            root.print();
        }
    }

    public void add(int i) {
        if (root == null) {
            root = new TreeNode(i);
        } else {
            root.add(i);
        }
    }
}
public interface PrintableTree {

    void add(int i);
    String prettyPrint();

    static PrintableTree getInstance() {
        return new TreeNode();
    }
}

Answer 1

Thank you for posting the rest of the code. Your issue is with the PrintableTree interface in method getInstance. You return a new TreeNode (it comes initialized with 0 as int is a primitive type and cannot be null). And then you add the rest of the nodes to that original node with 0. You most likely wanted to return a new BinaryTree instead. However you need to change your code as BinaryTree does not implement the PrintableTree interface.

Here are the changes necessary to fix it:

In PrintableTree.java

static PrintableTree getInstance() {
    return new BinaryTree();
}

In BinaryTree.java

// notice the added implements
class BinaryTree implements PrintableTree {
// the rest of the class is fine, add this to the end
    @Override
    public String prettyPrint() {
        if (root != null) {
            return root.prettyPrint();
        }
        return "";
    }
}

Also the class TreeNode does not need to extend BinaryTree as a node is not a tree (it doesn't make sense for the node the contain a value AND a root). If your assignment requires this relation then edit the code accordingly.