OnJava8-Examples/equalshashcode/SimpleHashMap.java at master · CSapprenticeWT/OnJava8-Examples · GitHub

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// equalshashcode/SimpleHashMap.java

// We make no guarantees that this code is fit for any purpose.

// Visit http://OnJava8.com for more book information.

// A demonstration hashed Map

import java.util.*;

import onjava.*;

public

class SimpleHashMap<K, V> extends AbstractMap<K, V> {

// Choose a prime number for the hash table

// size, to achieve a uniform distribution:

static final int SIZE = 997;

// You can't have a physical array of generics,

// but you can upcast to one:

@SuppressWarnings("unchecked")

LinkedList<MapEntry<K, V>>[] buckets =

new LinkedList[SIZE];

@Override public V put(K key, V value) {

V oldValue = null;

int index = Math.abs(key.hashCode()) % SIZE;

if(buckets[index] == null)

buckets[index] = new LinkedList<>();

LinkedList<MapEntry<K, V>> bucket = buckets[index];

MapEntry<K, V> pair = new MapEntry<>(key, value);

boolean found = false;

ListIterator<MapEntry<K, V>> it =

bucket.listIterator();

while(it.hasNext()) {

MapEntry<K, V> iPair = it.next();

if(iPair.getKey().equals(key)) {

oldValue = iPair.getValue();

it.set(pair); // Replace old with new

found = true;

break;

}

if(!found)

buckets[index].add(pair);

return oldValue;

}

@Override public V get(Object key) {

int index = Math.abs(key.hashCode()) % SIZE;

if(buckets[index] == null) return null;

for(MapEntry<K, V> iPair : buckets[index])

if(iPair.getKey().equals(key))

return iPair.getValue();

return null;

}

@Override public Set<Map.Entry<K, V>> entrySet() {

Set<Map.Entry<K, V>> set= new HashSet<>();

for(LinkedList<MapEntry<K, V>> bucket : buckets) {

if(bucket == null) continue;

for(MapEntry<K, V> mpair : bucket)

set.add(mpair);

}

return set;

}

public static void main(String[] args) {

SimpleHashMap<String,String> m =

new SimpleHashMap<>();

m.putAll(Countries.capitals(8));

m.forEach((k, v) ->

System.out.println(k + "=" + v));

System.out.println(m.get("BENIN"));

m.entrySet().forEach(System.out::println);

}

/* Output:

CAMEROON=Yaounde

ANGOLA=Luanda

BURKINA FASO=Ouagadougou

BURUNDI=Bujumbura

ALGERIA=Algiers

BENIN=Porto-Novo

CAPE VERDE=Praia

BOTSWANA=Gaberone

Porto-Novo