// onjava/CountMap.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Unlimited-length Map containing sample data
// {java onjava.CountMap}
package onjava;
import java.util.*;
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:
{0=A0, 1=B0, 2=C0, 3=D0, 4=E0, 5=F0, 6=G0, 7=H0, 8=I0,
9=J0, 10=K0, 11=L0, 12=M0, 13=N0, 14=O0, 15=P0, 16=Q0,
17=R0, 18=S0, 19=T0, 20=U0, 21=V0, 22=W0, 23=X0, 24=Y0,
25=Z0, 26=A1, 27=B1, 28=C1, 29=D1, 30=E1, 31=F1, 32=G1,
33=H1, 34=I1, 35=J1, 36=K1, 37=L1, 38=M1, 39=N1, 40=O1,
41=P1, 42=Q1, 43=R1, 44=S1, 45=T1, 46=U1, 47=V1, 48=W1,
49=X1, 50=Y1, 51=Z1, 52=A2, 53=B2, 54=C2, 55=D2, 56=E2,
57=F2, 58=G2, 59=H2}
G19
A0
B0
C0
D0
E0
F0

Y9
J21
R26
D33
Z36
N16
*/