Task: S-expressions
C#: using System;
using System.Collections.Generic;
using System.Text;

  public class SNode
    {
        private List<SNode> _items;
        public string Name { get; set; }
        public IReadOnlyCollection<SNode> Items { get { return _items.AsReadOnly(); } }
        public SNode()
        {
            this._items = new List<SNode>();
        }
        public SNode(string name):this()
        {
            this.Name=name;
        }
        public void AddNode(SNode node)
        {
            this._items.Add(node);
        }      
    }

    public class SNodeFull : SNode
    {
        private bool _isLeaf;
        public bool IsLeaf { get => _isLeaf; }
        public SNodeFull(bool isLeaf) : base()
        {
            this._isLeaf = isLeaf;
        }

        public SNodeFull(string name, bool isLeaf) : base(name)
        {
            this._isLeaf = isLeaf;
        }

        public SNodeFull RootNode { get; set; }

        public void AddNode(SNodeFull node)
        {
            base.AddNode(node);
            node.RootNode = this;
        }
    }

Java: package jfkbits;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;
import java.io.StreamTokenizer;
import java.io.StringReader;
import java.util.Iterator;

public class LispTokenizer implements Iterator<Token>
{
    
    StreamTokenizer m_tokenizer;
    IOException m_ioexn;

    
    public LispTokenizer(String src)
    {
        this(new StringReader(src));
    }

    
    public LispTokenizer(Reader r)
    {
        if(r == null)
            r = new StringReader("");
        BufferedReader buffrdr = new BufferedReader(r);
        m_tokenizer = new StreamTokenizer(buffrdr);
        m_tokenizer.resetSyntax(); 

        m_tokenizer.whitespaceChars(0, ' ');
        m_tokenizer.wordChars(' '+1,255);
        m_tokenizer.ordinaryChar('(');
        m_tokenizer.ordinaryChar(')');
        m_tokenizer.ordinaryChar('\'');
        m_tokenizer.commentChar(';');
        m_tokenizer.quoteChar('"');
    }

    public Token peekToken()
    {	
        if(m_ioexn != null)
            return null;
        try
        {
            m_tokenizer.nextToken();
        }
        catch(IOException e)
        {
            m_ioexn = e;
            return null;
        }
        if(m_tokenizer.ttype == StreamTokenizer.TT_EOF)
            return null;
        Token token = new Token(m_tokenizer);
        m_tokenizer.pushBack();
        return token;
    }

    public boolean hasNext()
    {
        if(m_ioexn != null)
            return false;
        try
        {
            m_tokenizer.nextToken();
        }
        catch(IOException e)
        {
            m_ioexn = e;
            return false;
        }
        if(m_tokenizer.ttype == StreamTokenizer.TT_EOF)
            return false;
        m_tokenizer.pushBack();
        return true;
    }

    
    public IOException getIOException()
    {
        return m_ioexn;
    }

    public Token next()
    {
        try
        {
            m_tokenizer.nextToken();
        }
        catch(IOException e)
        {
            m_ioexn = e;
            return null;
        }

        Token token = new Token(m_tokenizer);
        return token;
    }

    public void remove()
    {
    }
}