OnJava8-Examples/onjava/CountMap.java at master · CSapprenticeWT/OnJava8-Examples · GitHub

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// onjava/CountMap.java

// 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

J21

R26

D33

Z36

N16

OnJava8-Examples/onjava/CountMap.java at master · CSapprenticeWT/OnJava8-Examples · GitHub

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