Class CountMap

onjava/CountMap.java:11–67

import java.util.stream.*;

public class CountMap
extends AbstractMap<Integer,String> {
  private int size;
  private static char[] chars =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZ".toCharArray();
  private static String value(int key) {
    return
      chars[key % chars.length] +
      Integer.toString(key / chars.length);
  }
  public CountMap(int size) {
    this.size = size < 0 ? 0 : size;
  }
  @Override public String get(Object key) {
    return value((Integer)key);
  }
  private static class Entry
  implements Map.Entry<Integer,String> {
    int index;
    Entry(int index) { this.index = index; }
    @Override   public boolean equals(Object o) {
      return o instanceof Entry &&
        Objects.equals(index, ((Entry)o).index);
    }
    @Override public Integer getKey() { return index; }
    @Override public String getValue() {
      return value(index);
    }
    @Override public String setValue(String value) {
      throw new UnsupportedOperationException();
    }
    @Override public int hashCode() {
      return Objects.hashCode(index);
    }
  }
  @Override
  public Set<Map.Entry<Integer,String>> entrySet() {
    // LinkedHashSet retains initialization order:
    return IntStream.range(0, size)
      .mapToObj(Entry::new)
      .collect(Collectors
        .toCollection(LinkedHashSet::new));
  }
  public static void main(String[] args) {
    final int size = 6;
    CountMap cm = new CountMap(60);
    System.out.println(cm);
    System.out.println(cm.get(500));
    cm.values().stream()
      .limit(size)
      .forEach(System.out::println);
    System.out.println();
    new Random(47).ints(size, 0, 1000)
      .mapToObj(cm::get)
      .forEach(System.out::println);
  }
}
/* Output: