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anonymous /RobsHashMap
Created Nov 17, 2014

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Robs HashMap
package co.robl;
/**
* Created by Robbie on 17/11/2014.
* Simple Implementation of a HashMap
*/
public class RobsHashMap {
/* The initial size of the bucket array */
private int BUCKET_ARRAY_SIZE = 256;
private Node bucketArray[] = new Node[BUCKET_ARRAY_SIZE];
/* Constructors */
public RobsHashMap(){}
public RobsHashMap(int initialSize){
this.BUCKET_ARRAY_SIZE = initialSize;
}
/**
* Used to put a key-value pair into the data structure.
* @param key Key string that is used identify the key-value pair
* @param value Value string in which the key string maps to.
*/
public void put(String key, String value){
/* Get the hash code */
int hash = Math.abs(key.hashCode() % BUCKET_ARRAY_SIZE);
/* Create the Node to add to the linked list */
Node entry = new Node(key,value);
/* Insert the node to the bucket array at the hash index */
if(bucketArray[hash] == null){
/* No collision detected. Insert the node. */
bucketArray[hash] = entry;
}else{
/* Collision detected. We must place the node at the end of the linked list. */
Node current = bucketArray[hash];
while(current.next != null){
/* Check if the key already exists */
if(current.getKey().equals(entry.getKey())){
/* Replace the keys value with the new one */
current.setValue(entry.getValue());
return;
}
current = current.next;
}
/* When the code gets here current.next == null */
/* Insert the node */
current.next = entry;
}
}
/**
* Returns the value that is mapped to the give key.
* @param key The key string which is used to search for the value it
* is mapped to.
* @return The value string
*/
public String get(String key){
/* Get the hash */
int hash = Math.abs(key.hashCode() % BUCKET_ARRAY_SIZE);
/* Search for key in linked list */
Node n = bucketArray[hash];
/* Traverse linked list */
while(n != null){
if(n.getKey().equals(key)){
return n.getValue();
}
n = n.getNext();
}
/* Not found? then return null */
return null;
}
/* This is the simple object that we use to store each key-value pair */
class Node{
private String key;
private String value;
private Node next;
public Node(){}
public Node(String key, String value){
this.key = key;
this.value = value;
}
public String getKey() {
return key;
}
public void setKey(String key) {
this.key = key;
}
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
public Node getNext() {
return next;
}
public void setNext(Node next) {
this.next = next;
}
}
}
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