// PathIterator.java

package javaiterator;

import java.util.Iterator;

public class PathIterator implements Iterator<String> {

    private final String string;
    private int index;

    public PathIterator(String s) { string = s; index = -1; }

    @Override
    public boolean hasNext() { return index < string.length(); }

    @Override
    public String next() {
        int start = index, length = string.length();
        char ch;
        while(++index < length && (ch = string.charAt(index)) != '.')
            if(ch == '[') index = getIndexOfCloseBraket(string, index);
        return trimBrakets(string.substring(++start, index));
    }

    public static String trimBrakets(String s)
    {
        int start = 0, length = s.length();
        if(--length < 0) return s;
        while(s.charAt(start) == '[' &&
            getIndexOfCloseBraket(s, start) == length)
        {
            ++start;
            --length;
        }
        return s.substring(start, ++length);
    }

    public static int getIndexOfCloseBraket(String s, int open) {
        int brakets = 1, length = s.length();
        char ch;
        while(++open < length && brakets > 0)
            if((ch = s.charAt(open)) == '[') ++brakets;
            else if(ch == ']') --brakets;
        return --open;
    }
}

        while(iterator.hasNext())
            System.out.println(iterator.next());

        while(iterator.hasNext())
            System.out.println(iterator.next()
                .replaceAll("\\[", "").replaceAll("\\]", ""));

 private static String filter(String input) {
        if (input == null || input.isEmpty()) {
            return input;
        }
        StringBuilder out = new StringBuilder(input.length());
        int openedBraces = 0;
        for (int i = 0; i < input.length(); i++) {
            char c = input.charAt(i);
            switch (c) {
                case '[':
                    openedBraces++;
                    break;
                case ']':
                    if (openedBraces > 0) {
                        openedBraces--;
                    } else {
                        throw new IllegalArgumentException("Unexpected closing brace at " + i);
                    }
                    break;
                case '.':
                    if (openedBraces > 0) {
                        out.append(c);
                    }
                    else {
                        out.append(" ");
                    }
                    break;
                default:
                    out.append(c);
                    break;
            }
        }
        return out.toString();
    }