[Java][АПС] - Recursive PostOrder

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;

class BNode<E> {

    public E info;
    public BNode<E> left;
    public BNode<E> right;

    static int LEFT = 1;
    static int RIGHT = 2;

    public BNode(E info) {
        this.info = info;
        left = null;
        right = null;
    }

    public BNode() {
        this.info = null;
        left = null;
        right = null;
    }

    public BNode(E info, BNode<E> left, BNode<E> right) {
        this.info = info;
        this.left = left;
        this.right = right;
    }

}

class BTree<E> {

    public BNode<E> root;

    public BTree() {
        root = null;
    }

    public BTree(E info) {
        root = new BNode<E>(info);
    }

    public void makeRoot(E elem) {
        root = new BNode(elem);
    }

    public void makeRootNode(BNode<E> node) {
        root = node;
    }

    public BNode<E> addChild(BNode<E> node, int where, E elem) {

        BNode<E> tmp = new BNode<E>(elem);

        if (where == BNode.LEFT) {
            if (node.left != null)  // veke postoi element
                return null;
            node.left = tmp;
        } else {
            if (node.right != null) // veke postoi element
                return null;
            node.right = tmp;
        }

        return tmp;
    }

    public BNode<E> addChildNode(BNode<E> node, int where, BNode<E> tmp) {

        if (where == BNode.LEFT) {
            if (node.left != null)  // veke postoi element
                return null;
            node.left = tmp;
        } else {
            if (node.right != null) // veke postoi element
                return null;
            node.right = tmp;
        }

        return tmp;
    }

    public void printPostOrder(BNode<E> node) {
    	if(node==null)
    		return ;
    	if(node.left!=null) {
    		printPostOrder(node.left);
    	}
    	if(node.right!=null) {
    		printPostOrder(node.right);
    	}
    	System.out.println(node.info);
    }
}
public class PostOrder {

	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		int n = Integer.parseInt(br.readLine());
		StringTokenizer st;

		BNode<String> [] nodes = new BNode[n];
		for(int i=0;i<n;i++) {
			nodes[i] = new BNode<String>();
		}

		BTree<String> tree = new BTree<String>();
		for(int i=0;i<n;i++) {
			String line = br.readLine();
			st = new StringTokenizer(line);
			int index = Integer.parseInt(st.nextToken());
			nodes[index].info = st.nextToken();
			String action = st.nextToken();
			if(action.equals("LEFT")) {
				tree.addChildNode(nodes[Integer.parseInt(st.nextToken())], BNode.LEFT, nodes[index]);
			}
			else if(action.equals("RIGHT")) {
				tree.addChildNode(nodes[Integer.parseInt(st.nextToken())], BNode.RIGHT, nodes[index]);
			}
			else {
				tree.makeRootNode(nodes[index]);
			}
		}
		tree.printPostOrder(tree.root);
	}

}