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Employee object overrides:
>equals method - helps in checking equality of employee objects used as key in entry objects.
>hashCode method - helps in finding bucket’s index on which data will be stored.
@Override
public boolean equals(Object o){
if(o==null)
return false;
if(this.getClass()!=o.getClass())
return false;
Employee e=(Employee)o;
return e.id.equals(this.id) && e.name.equals(this.name);
}
@Override
public int hashCode(){
return id.hashCode() + name.hashCode();
}
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Must read: LinkedHashMap Custom implementation
2) Full Program/SourceCode to put, get, remove Employee object in own/custom HashMap>
package com.ankit;
/** Copyright (c), AnkitMittal JavaMadeSoEasy.com */
/**
* @author AnkitMittal
* Copyright (c), AnkitMittal . All Contents are copyrighted and must not be reproduced in any form.
* Employee class- to be used as key in HashMapCustom.
*/
class Employee {
private String id;
private String name;
/**
* Employee constructor
*/
public Employee(String id, String name) { // constructor
this.id = id;
this.name = name;
}
@Override
public String toString() {
return "Employee[id=" + id + ", name=" + name + "] ";
}
@Override
public boolean equals(Object o){
if(o==null)
return false;
if(this.getClass()!=o.getClass())
return false;
Employee e=(Employee)o;
return e.id.equals(this.id) && e.name.equals(this.name);
}
@Override
public int hashCode(){
return id.hashCode() + name.hashCode();
}
}
/** Copyright (c), AnkitMittal JavaMadeSoEasy.com */
/**
* @author AnkitMittal
* Copyright (c), AnkitMittal . All Contents are copyrighted and must not be reproduced in any form.
* This class provides custom implementation of HashMap(without using java api's)- which allows us to store data in key-value pair form.
* insertion order of key-value pairs is not maintained.
* @param <K>
* @param <V>
*/
class HashMapCustom<K, V> {
private Entry<K,V>[] table; //Array of Entry.
private int capacity= 4; //Initial capacity of HashMap
static class Entry<K, V> {
K key;
V value;
Entry<K,V> next;
public Entry(K key, V value, Entry<K,V> next){
this.key = key;
this.value = value;
this.next = next;
}
}
@SuppressWarnings("unchecked")
public HashMapCustom(){
table = new Entry[capacity];
}
/**
* Method allows you put key-value pair in HashMapCustom.
* If the map already contains a mapping for the key, the old value is replaced.
* Note: method does not allows you to put null key thought it allows null values.
* Implementation allows you to put custom objects as a key as well.
* Key Features: implementation provides you with following features:-
* >provide complete functionality how to override equals method.
* >provide complete functionality how to override hashCode method.
* @param newKey
* @param data
*/
public void put(K newKey, V data){
if(newKey==null)
return; //does not allow to store null.
int hash=hash(newKey);
Entry<K,V> newEntry = new Entry<K,V>(newKey, data, null);
if(table[hash] == null){
table[hash] = newEntry;
}else{
Entry<K,V> previous = null;
Entry<K,V> current = table[hash];
while(current != null){ //we have reached last entry of bucket.
if(current.key.equals(newKey)){
if(previous==null){ //node has to be insert on first of bucket.
newEntry.next=current.next;
table[hash]=newEntry;
return;
}
else{
newEntry.next=current.next;
previous.next=newEntry;
return;
}
}
previous=current;
current = current.next;
}
previous.next = newEntry;
}
}
/**
* Method returns value corresponding to key.
* @param key
*/
public V get(K key){
int hash = hash(key);
if(table[hash] == null){
return null;
}else{
Entry<K,V> temp = table[hash];
while(temp!= null){
if(temp.key.equals(key))
return temp.value;
temp = temp.next; //return value corresponding to key.
}
return null; //returns null if key is not found.
}
}
/**
* Method removes key-value pair from HashMapCustom.
* @param key
*/
public boolean remove(K deleteKey){
int hash=hash(deleteKey);
if(table[hash] == null){
return false;
}else{
Entry<K,V> previous = null;
Entry<K,V> current = table[hash];
while(current != null){ //we have reached last entry node of bucket.
if(current.key.equals(deleteKey)){
if(previous==null){ //delete first entry node.
table[hash]=table[hash].next;
return true;
}
else{
previous.next=current.next;
return true;
}
}
previous=current;
current = current.next;
}
return false;
}
}
/**
* Method displays all key-value pairs present in HashMapCustom.,
* insertion order is not guaranteed, for maintaining insertion order refer LinkedHashMapCustom.
* @param key
*/
public void display(){
for(int i=0;i<capacity;i++){
if(table[i]!=null){
Entry<K, V> entry=table[i];
while(entry!=null){
System.out.print("{"+entry.key+"="+entry.value+"}" +" ");
entry=entry.next;
}
}
}
}
/**
* Method implements hashing functionality, which helps in finding the appropriate bucket location to store our data.
* This is very important method, as performance of HashMapCustom is very much dependent on this method's implementation.
* @param key
*/
private int hash(K key){
return Math.abs(key.hashCode()) % capacity;
}
}
/**
* Main class- to test HashMap functionality.
*/
public class HashMapCustomEmp {
public static void main(String[] args) {
HashMapCustom<Employee, Integer> hashMapCustom = new HashMapCustom<Employee, Integer>();
hashMapCustom.put(new Employee("10", "sam"), 12);
hashMapCustom.put(new Employee("21", "amy"), 121);
hashMapCustom.put(new Employee("31", "rob"), 151);
hashMapCustom.put(new Employee("41", "sam"), 15);
hashMapCustom.put(new Employee("42", "wil"), 89);
System.out.println("Display values corresponding to keys>");
System.out.println("value corresponding to employee with id=21 & name='amy' : "+hashMapCustom.get(new Employee("21", "amy")));
System.out.println("value corresponding to employee with id=51 & name='pat' : "+hashMapCustom.get(new Employee("51", "pat")));
System.out.print("Displaying : ");
hashMapCustom.display();
System.out.println("\n\nvalue corresponding to employee with id=21 & name='amy' removed: "+hashMapCustom.remove(new Employee("21", "amy")));
System.out.println("value corresponding to employee with id=51 & name='pat' removed: "+hashMapCustom.remove(new Employee("51", "pat")));
System.out.print("Displaying : ");
hashMapCustom.display();
}
}
/*Output
Display values corresponding to keys>
value corresponding to employee with id=21 & name='amy' : 121
value corresponding to employee with id=51 & name='pat' : null
Displaying : {Employee[id=21, name=amy] =121} {Employee[id=41, name=sam] =15} {Employee[id=42, name=wil] =89} {Employee[id=10, name=sam] =12} {Employee[id=31, name=rob] =151}
value corresponding to employee with id=21 & name='amy' removed: true
value corresponding to employee with id=51 & name='pat' removed: false
Displaying : {Employee[id=41, name=sam] =15} {Employee[id=42, name=wil] =89} {Employee[id=10, name=sam] =12} {Employee[id=31, name=rob] =151}
*/
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