Main.java

package com.grisha.tree;

import java.io.*;
import java.util.ArrayList;
import java.util.List;

public class Main {
    public static Node createTmpTree() {
        Node animal = new Node("Animal");
        Node bear = new Node("Bear");
        Node cat = new Node("Cat");
        Node dog = new Node("Dog");
        Node jaguar = new Node("Jaguar");
        Node panther = new Node("Panther");
        Node lynx = new Node("Lynx");
        Node wolf = new Node("Wolf");
        Node dingo = new Node("Dingo");

        animal.addChild(cat);
        animal.addChild(dog);
        animal.addChild(bear);

        cat.addChild(jaguar);
        cat.addChild(panther);
        cat.addChild(lynx);

        dog.addChild(wolf);
        dog.addChild(dingo);

        return animal;
    }

    private static String treeToString(Node node) {
        String strTree = node.getValue() + ">(";
        List<Node> children = node.getChildren();
        for (Node child : children) {
            if (child.getChildren().size() > 0) {
                strTree += treeToString(child);
            }
            else  {
                strTree += child.getValue();
            }
            strTree += children.indexOf(child) == children.size() - 1 ? ")" : ",";
        }
        return strTree;
    }

    public static String printTree(Node node) {
        String strTree = treeToString(node);
        System.out.println(strTree);
        return strTree;
    }

    public static void writeTree(Node node, String dir, String filename) {
        String strTree = printTree(node);
        BufferedWriter output = null;
        try {
            File file = new File(dir, filename);
            output = new BufferedWriter(new FileWriter(file));
            output.write(strTree);
            output.close();
        } catch ( IOException e ) {
            e.printStackTrace();
        }
    }

    public static String reedTree(String dir, String filename) {
        BufferedReader input = null;
        String path = dir + "/" + filename;
        String strTree = "";
        try {
            String line;
            input = new BufferedReader(new FileReader(path));
            strTree = input.readLine();
            input.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return strTree;
    }

    private static List<Integer> getIndexOdChild(String childrenStr) {
        List<Integer> indexArray = new ArrayList<>();
        int open = 0;
        int close = 0;
        indexArray.add(0);
        for (int i = 0; i < childrenStr.length(); i++) {
            char cur = childrenStr.charAt(i);
            if (cur == '(') {
                open++;
            }
            else if (cur == ')'){
                close++;
            }
            else if (cur == ',' && open == close){
                open = 0;
                close = 0;
                indexArray.add(i);
            }
        }
        indexArray.add(childrenStr.length());
        return indexArray;
    }

    private static List<String> splitChildren(String childrenStr) {
        List<String> childrenArray = new ArrayList<>();
        if (childrenStr.indexOf('(') == -1) {
            for (String part : childrenStr.split(",")) {
                childrenArray.add(part);
            }
        }
        else {
            List<Integer> indexArray = getIndexOdChild(childrenStr);
            for (int i = 0; i < indexArray.size() - 1; i++) {
                String substring = childrenStr.substring(indexArray.get(i) + (i == 0 ? 0 : 1), indexArray.get(i + 1));
                childrenArray.add(substring);
            }
        }
        return childrenArray;
    }

    public static Node stringToTree(String strTree) {
        String[] parts = strTree.split(">", 2);
        Node node = new Node(parts[0]);
        if (parts.length == 1) {
            return node;
        }
        String childrenStr = parts[1].substring(1, parts[1].length() - 1);
        List<String> childrenArray = splitChildren(childrenStr);
        for (int i = 0; i < childrenArray.size(); i++) {
            node.addChild(stringToTree(childrenArray.get(i)));
        }
        return node;
    }

    public static void main(String[] args) {
        String dir = "/Users/Gregory/IdeaProjects/java.lessons/lesson1/src/main/java/com/grisha/tree";
        String filename = "tmp.txt";

        Node tree = createTmpTree();
        writeTree(tree, dir, filename);

        String strTree = reedTree(dir, filename);

        Node newTree = stringToTree(strTree);
        printTree(newTree);
    }
}

Node.java

package com.grisha.tree;

import java.util.ArrayList;
import java.util.List;

public class Node {
    private String value;
    private List<Node> children = new ArrayList<>();

    public Node(String initValue) {
        value = initValue;
    }

    public void setValue (String newValue) {
        value = newValue;
    }

    public String getValue () {
        return value;
    }

    public void setChildren(List newChildren) {
        children = newChildren;
    }

    public List getChildren () {
        return children;
    }

    public void addChild(Node child) {
        children.add(child);
    }
}