Comparing the CR plate number iterators

PlateNumberIterable.java

import java.util.Iterator;
import java.util.NoSuchElementException;

public final class PlateNumberIterable implements Iterable<String> {

    @Override
    public Iterator<String> iterator() {
        return new PlateNumberIterator();
    }
    
    private static final class PlateNumberIterator implements Iterator<String> {

        private static final int NUMBER_OF_ALL_CANDIDATE_PLATE_NUMBERS = 
                26 * 26 * 26 * 10_000;
        
        private static final int NUMBER_OF_ALL_SKIPPED_PLATE_NUMBERS = 
                26 * 26 * 26;
        
        private static final int NUMBER_OF_TOTAL_LEGAL_PLATE_NUMBERS = 
                NUMBER_OF_ALL_CANDIDATE_PLATE_NUMBERS - 
                NUMBER_OF_ALL_SKIPPED_PLATE_NUMBERS; 
        
        private int numberOfIteratedPlates = 0;
        
        private final char[] chars = 
                new char[]{ 'A', 'A', 'A', '0', '0', '0', '1' };
        
        @Override
        public boolean hasNext() {
            return numberOfIteratedPlates < NUMBER_OF_TOTAL_LEGAL_PLATE_NUMBERS;
        }

        @Override
        public String next() {
            if (!hasNext()) {
                throw new NoSuchElementException("Iterator exhausted.");
            }
            
            numberOfIteratedPlates++;
            String result = new String(chars);
            incrementPlateNumber();
            return result;
        }

        private void incrementPlateNumber() {
            for (int i = 6; i >= 3; i--) {
                if (chars[i] < '9') {
                    chars[i]++;

                    for (int j = i + 1; j < 7; j++) {
                        chars[j] = '0';
                    }

                    return;
                }
            }

            chars[3] =
            chars[4] =
            chars[5] = '0';
            chars[6] = '1';

            for (int i = 2; i >= 0; i--) {
                if (chars[i] < 'Z') {
                    chars[i]++;

                    for (int j = i + 1; j < 3; j++) {
                        chars[j] = 'A';
                    }

                    return;
                }
            }
        }
    }
    
    public static void main(String[] args) {
        int coderoddePlates = 0;
        long start = System.currentTimeMillis();
        
        for (String plateNumber : new PlateNumberIterable()) {
            coderoddePlates++;
        }
        
        long end = System.currentTimeMillis();
        
        System.out.println("coderodde iterable computation time: " + 
                (end - start) + " ms.");
        
        int AJNeufeldPlates = 0;
        start = System.currentTimeMillis();
        
        for (String plateNumber : new Plates("AAA0001")) {
            AJNeufeldPlates++;
        }
        
        end = System.currentTimeMillis();
        
        System.out.println("AJNeufeld iterable computation time: " +
                (end - start) + " ms.");
        
        System.out.println("coderodde iterable produced " + coderoddePlates +
                " plates.");
        
        System.out.println("AJNeufeld iterable produced " + AJNeufeldPlates +
                " plates.");
    }
}

Plates.java

import java.util.Iterator;

public class Plates implements Iterable<String> {
    
    private final String initial_plate;
    
    public Plates(String first_plate) {
        initial_plate = first_plate;
    }
    
    @Override
    public Iterator<String> iterator() {
        return new PlateIterator(initial_plate);
    }
    
    private static class PlateIterator implements Iterator<String> {
        private final int plate_length;
        private final StringBuilder plate;
        private boolean has_next = true;
        private boolean need_next = false;
        
        PlateIterator(String first_plate) {
            plate_length = first_plate.length();
            plate = new StringBuilder(plate_length);
            plate.append(first_plate);
            has_next = true;
            need_next = false;
        }
    
        private void advance() {
            need_next = false;
            has_next = false;
            for (int i = plate_length - 1; i >= 0; i--) {
                char ch = plate.charAt(i);
                if (ch == '9')
                    plate.setCharAt(i, '0');
                else if (ch == 'Z')
                    plate.setCharAt(i,  'A');
                else {
                    plate.setCharAt(i, (char) (ch + 1));
                    has_next = true;
                    break;
                }
            }
            if (plate.substring(plate_length - 4).equals("0000"))
                plate.setCharAt(plate_length - 1, '1');
        }
    
        @Override
        public boolean hasNext() {
            if (has_next && need_next)
                advance();
            return has_next;
        }
    
        @Override
        public String next() {
            if (need_next)
                advance();
            need_next = true;
            return plate.toString();
        }
    }
}