TimeZone Ids In Java and Date Serialization with TimeZone using Jackson

1. There are total of 617 number  of  supported time zone IDs  available in the JDK version 1.8  and following is the list of all the IDs obtained from the java.util.TimeZone  :
--------------------

Africa/Abidjan

Africa/Accra

Africa/Addis_Ababa

Africa/Algiers

Africa/Asmara

Africa/Asmera

Africa/Bamako

Africa/Bangui

Africa/Banjul

Africa/Bissau

Africa/Blantyre

Africa/Brazzaville

Africa/Bujumbura

Africa/Cairo

Africa/Casablanca

Africa/Ceuta

Africa/Conakry

Africa/Dakar

Africa/Dar_es_Salaam

Africa/Djibouti

Africa/Douala

Africa/El_Aaiun

Africa/Freetown

Africa/Gaborone

Africa/Harare

Africa/Johannesburg

Africa/Juba

Africa/Kampala

Africa/Khartoum

Africa/Kigali

Africa/Kinshasa

Africa/Lagos

Africa/Libreville

Africa/Lome

Africa/Luanda

Africa/Lubumbashi

Africa/Lusaka

Africa/Malabo

Africa/Maputo

Africa/Maseru

Africa/Mbabane

Africa/Mogadishu

Africa/Monrovia

Africa/Nairobi

Africa/Ndjamena

Africa/Niamey

Africa/Nouakchott

Africa/Ouagadougou

Africa/Porto-Novo

Africa/Sao_Tome

Africa/Timbuktu

Africa/Tripoli

Africa/Tunis

Africa/Windhoek

America/Adak

America/Anchorage

America/Anguilla

America/Antigua

America/Araguaina

America/Argentina/Buenos_Aires

America/Argentina/Catamarca

America/Argentina/ComodRivadavia

America/Argentina/Cordoba

America/Argentina/Jujuy

America/Argentina/La_Rioja

America/Argentina/Mendoza

America/Argentina/Rio_Gallegos

America/Argentina/Salta

America/Argentina/San_Juan

America/Argentina/San_Luis

America/Argentina/Tucuman

America/Argentina/Ushuaia

America/Aruba

America/Asuncion

America/Atikokan

America/Atka

America/Bahia

America/Bahia_Banderas

America/Barbados

America/Belem

America/Belize

America/Blanc-Sablon

America/Boa_Vista

America/Bogota

America/Boise

America/Buenos_Aires

America/Cambridge_Bay

America/Campo_Grande

America/Cancun

America/Caracas

America/Catamarca

America/Cayenne

America/Cayman

America/Chicago

America/Chihuahua

America/Coral_Harbour

America/Cordoba

America/Costa_Rica

America/Creston

America/Cuiaba

America/Curacao

America/Danmarkshavn

America/Dawson

America/Dawson_Creek

America/Denver

America/Detroit

America/Dominica

America/Edmonton

America/Eirunepe

America/El_Salvador

America/Ensenada

America/Fort_Wayne

America/Fortaleza

America/Glace_Bay

America/Godthab

America/Goose_Bay

America/Grand_Turk

America/Grenada

America/Guadeloupe

America/Guatemala

America/Guayaquil

America/Guyana

America/Halifax

America/Havana

America/Hermosillo

America/Indiana/Indianapolis

America/Indiana/Knox

America/Indiana/Marengo

America/Indiana/Petersburg

America/Indiana/Tell_City

America/Indiana/Vevay

America/Indiana/Vincennes

America/Indiana/Winamac

America/Indianapolis

America/Inuvik

America/Iqaluit

America/Jamaica

America/Jujuy

America/Juneau

America/Kentucky/Louisville

America/Kentucky/Monticello

America/Knox_IN

America/Kralendijk

America/La_Paz

America/Lima

America/Los_Angeles

America/Louisville

America/Lower_Princes

America/Maceio

America/Managua

America/Manaus

America/Marigot

America/Martinique

America/Matamoros

America/Mazatlan

America/Mendoza

America/Menominee

America/Merida

America/Metlakatla

America/Mexico_City

America/Miquelon

America/Moncton

America/Monterrey

America/Montevideo

America/Montreal

America/Montserrat

America/Nassau

America/New_York

America/Nipigon

America/Nome

America/Noronha

America/North_Dakota/Beulah

America/North_Dakota/Center

America/North_Dakota/New_Salem

America/Ojinaga

America/Panama

America/Pangnirtung

America/Paramaribo

America/Phoenix

America/Port-au-Prince

America/Port_of_Spain

America/Porto_Acre

America/Porto_Velho

America/Puerto_Rico

America/Rainy_River

America/Rankin_Inlet

America/Recife

America/Regina

America/Resolute

America/Rio_Branco

America/Rosario

America/Santa_Isabel

America/Santarem

America/Santiago

America/Santo_Domingo

America/Sao_Paulo

America/Scoresbysund

America/Shiprock

America/Sitka

America/St_Barthelemy

America/St_Johns

America/St_Kitts

America/St_Lucia

America/St_Thomas

America/St_Vincent

America/Swift_Current

America/Tegucigalpa

America/Thule

America/Thunder_Bay

America/Tijuana

America/Toronto

America/Tortola

America/Vancouver

America/Virgin

America/Whitehorse

America/Winnipeg

America/Yakutat

America/Yellowknife

Antarctica/Casey

Antarctica/Davis

Antarctica/DumontDUrville

Antarctica/Macquarie

Antarctica/Mawson

Antarctica/McMurdo

Antarctica/Palmer

Antarctica/Rothera

Antarctica/South_Pole

Antarctica/Syowa

Antarctica/Troll

Antarctica/Vostok

Arctic/Longyearbyen

Asia/Aden

Asia/Almaty

Asia/Amman

Asia/Anadyr

Asia/Aqtau

Asia/Aqtobe

Asia/Ashgabat

Asia/Ashkhabad

Asia/Baghdad

Asia/Bahrain

Asia/Baku

Asia/Bangkok

Asia/Beirut

Asia/Bishkek

Asia/Brunei

Asia/Calcutta

Asia/Chita

Asia/Choibalsan

Asia/Chongqing

Asia/Chungking

Asia/Colombo

Asia/Dacca

Asia/Damascus

Asia/Dhaka

Asia/Dili

Asia/Dubai

Asia/Dushanbe

Asia/Gaza

Asia/Harbin

Asia/Hebron

Asia/Ho_Chi_Minh

Asia/Hong_Kong

Asia/Hovd

Asia/Irkutsk

Asia/Istanbul

Asia/Jakarta

Asia/Jayapura

Asia/Jerusalem

Asia/Kabul

Asia/Kamchatka

Asia/Karachi

Asia/Kashgar

Asia/Kathmandu

Asia/Katmandu

Asia/Khandyga

Asia/Kolkata

Asia/Krasnoyarsk

Asia/Kuala_Lumpur

Asia/Kuching

Asia/Kuwait

Asia/Macao

Asia/Macau

Asia/Magadan

Asia/Makassar

Asia/Manila

Asia/Muscat

Asia/Nicosia

Asia/Novokuznetsk

Asia/Novosibirsk

Asia/Omsk

Asia/Oral

Asia/Phnom_Penh

Asia/Pontianak

Asia/Pyongyang

Asia/Qatar

Asia/Qyzylorda

Asia/Rangoon

Asia/Riyadh

Asia/Saigon

Asia/Sakhalin

Asia/Samarkand

Asia/Seoul

Asia/Shanghai

Asia/Singapore

Asia/Srednekolymsk

Asia/Taipei

Asia/Tashkent

Asia/Tbilisi

Asia/Tehran

Asia/Tel_Aviv

Asia/Thimbu

Asia/Thimphu

Asia/Tokyo

Asia/Ujung_Pandang

Asia/Ulaanbaatar

Asia/Ulan_Bator

Asia/Urumqi

Asia/Ust-Nera

Asia/Vientiane

Asia/Vladivostok

Asia/Yakutsk

Asia/Yekaterinburg

Asia/Yerevan

Atlantic/Azores

Atlantic/Bermuda

Atlantic/Canary

Atlantic/Cape_Verde

Atlantic/Faeroe

Atlantic/Faroe

Atlantic/Jan_Mayen

Atlantic/Madeira

Atlantic/Reykjavik

Atlantic/South_Georgia

Atlantic/St_Helena

Atlantic/Stanley

Australia/ACT

Australia/Adelaide

Australia/Brisbane

Australia/Broken_Hill

Australia/Canberra

Australia/Currie

Australia/Darwin

Australia/Eucla

Australia/Hobart

Australia/LHI

Australia/Lindeman

Australia/Lord_Howe

Australia/Melbourne

Australia/NSW

Australia/North

Australia/Perth

Australia/Queensland

Australia/South

Australia/Sydney

Australia/Tasmania

Australia/Victoria

Australia/West

Australia/Yancowinna

Brazil/Acre

Brazil/DeNoronha

Brazil/East

Brazil/West

CET

CST6CDT

Canada/Atlantic

Canada/Central

Canada/East-Saskatchewan

Canada/Eastern

Canada/Mountain

Canada/Newfoundland

Canada/Pacific

Canada/Saskatchewan

Canada/Yukon

Chile/Continental

Chile/EasterIsland

Cuba

EET

EST5EDT

Egypt

Eire

Etc/GMT

Etc/GMT+0

Etc/GMT+1

Etc/GMT+10

Etc/GMT+11

Etc/GMT+12

Etc/GMT+2

Etc/GMT+3

Etc/GMT+4

Etc/GMT+5

Etc/GMT+6

Etc/GMT+7

Etc/GMT+8

Etc/GMT+9

Etc/GMT-0

Etc/GMT-1

Etc/GMT-10

Etc/GMT-11

Etc/GMT-12

Etc/GMT-13

Etc/GMT-14

Etc/GMT-2

Etc/GMT-3

Etc/GMT-4

Etc/GMT-5

Etc/GMT-6

Etc/GMT-7

Etc/GMT-8

Etc/GMT-9

Etc/GMT0

Etc/Greenwich

Etc/UCT

Etc/UTC

Etc/Universal

Etc/Zulu

Europe/Amsterdam

Europe/Andorra

Europe/Athens

Europe/Belfast

Europe/Belgrade

Europe/Berlin

Europe/Bratislava

Europe/Brussels

Europe/Bucharest

Europe/Budapest

Europe/Busingen

Europe/Chisinau

Europe/Copenhagen

Europe/Dublin

Europe/Gibraltar

Europe/Guernsey

Europe/Helsinki

Europe/Isle_of_Man

Europe/Istanbul

Europe/Jersey

Europe/Kaliningrad

Europe/Kiev

Europe/Lisbon

Europe/Ljubljana

Europe/London

Europe/Luxembourg

Europe/Madrid

Europe/Malta

Europe/Mariehamn

Europe/Minsk

Europe/Monaco

Europe/Moscow

Europe/Nicosia

Europe/Oslo

Europe/Paris

Europe/Podgorica

Europe/Prague

Europe/Riga

Europe/Rome

Europe/Samara

Europe/San_Marino

Europe/Sarajevo

Europe/Simferopol

Europe/Skopje

Europe/Sofia

Europe/Stockholm

Europe/Tallinn

Europe/Tirane

Europe/Tiraspol

Europe/Uzhgorod

Europe/Vaduz

Europe/Vatican

Europe/Vienna

Europe/Vilnius

Europe/Volgograd

Europe/Warsaw

Europe/Zagreb

Europe/Zaporozhye

Europe/Zurich

GB

GB-Eire

GMT

GMT0

Greenwich

Hongkong

Iceland

Indian/Antananarivo

Indian/Chagos

Indian/Christmas

Indian/Cocos

Indian/Comoro

Indian/Kerguelen

Indian/Mahe

Indian/Maldives

Indian/Mauritius

Indian/Mayotte

Indian/Reunion

Iran

Israel

Jamaica

Japan

Kwajalein

Libya

MET

MST7MDT

Mexico/BajaNorte

Mexico/BajaSur

Mexico/General

NZ

NZ-CHAT

Navajo

PRC

PST8PDT

Pacific/Apia

Pacific/Auckland

Pacific/Bougainville

Pacific/Chatham

Pacific/Chuuk

Pacific/Easter

Pacific/Efate

Pacific/Enderbury

Pacific/Fakaofo

Pacific/Fiji

Pacific/Funafuti

Pacific/Galapagos

Pacific/Gambier

Pacific/Guadalcanal

Pacific/Guam

Pacific/Honolulu

Pacific/Johnston

Pacific/Kiritimati

Pacific/Kosrae

Pacific/Kwajalein

Pacific/Majuro

Pacific/Marquesas

Pacific/Midway

Pacific/Nauru

Pacific/Niue

Pacific/Norfolk

Pacific/Noumea

Pacific/Pago_Pago

Pacific/Palau

Pacific/Pitcairn

Pacific/Pohnpei

Pacific/Ponape

Pacific/Port_Moresby

Pacific/Rarotonga

Pacific/Saipan

Pacific/Samoa

Pacific/Tahiti

Pacific/Tarawa

Pacific/Tongatapu

Pacific/Truk

Pacific/Wake

Pacific/Wallis

Pacific/Yap

Poland

Portugal

ROK

Singapore

SystemV/AST4

SystemV/AST4ADT

SystemV/CST6

SystemV/CST6CDT

SystemV/EST5

SystemV/EST5EDT

SystemV/HST10

SystemV/MST7

SystemV/MST7MDT

SystemV/PST8

SystemV/PST8PDT

SystemV/YST9

SystemV/YST9YDT

Turkey

UCT

US/Alaska

US/Aleutian

US/Arizona

US/Central

US/East-Indiana

US/Eastern

US/Hawaii

US/Indiana-Starke

US/Michigan

US/Mountain

US/Pacific

US/Pacific-New

US/Samoa

UTC

Universal

W-SU

WET

Zulu

EST

HST

MST

ACT

AET

AGT

ART

AST

BET

BST

CAT

CNT

CST

CTT

EAT

ECT

IET

IST

JST

MIT

NET

NST

PLT

PNT

PRT

PST

SST

VST

-----------------------

2. In the Jackson setting the Timezone can help in the serialization of the Date data correct with the given timezone , there are two ways of setting the timezone for Jackson frequently used in the Spring framework : 

a) Using Object wrapper : 

         ObjectMapper mapper = new ObjectMapper();

         DateFormat dateFormat = new SimpleDateFormat("dd-MM-yyyy'T'HH:mm:ss.SSSZ");

         dateFormat.setTimeZone(TimeZone.getTimeZone("IST"));

         mapper.setDateFormat(dateFormat);

b)  In the  Jackson 2.x version using the  annotation : 

@JsonFormat(shape=JsonFormat.Shape.STRING,pattern="dd-MM-yyyy'T'HH:mm:ss.SSSZ", timezone="IST")

private Date date;

Anagram

An anagram is a type of wordplay, the result of rearranging the letters of a word or phrase to produce a new word or phrase, using all the original letters exactly once.

Example is "silent" which can be rearranged to "listen"

Question arises to find out whether two given strings are Anagram or not??

There can be multiple ways of solving the problems and most optimal solution would be using least time complexity and space. O(1) is the best and  denotes constant  time complexity , O(n) can be better etc..

Couple of solution is given as follows : 

**

 * @author sachin

 *

 */

public class Anagram {

public static void main(String[] args) {

String firstString = "silent";

String secondString = "listen";

System.out.println(isAnagram1(firstString, secondString));

System.out.println(isAnagram2(firstString, secondString));

//isAnagram1()  method gives solution in time complexity of O(nlogn)

//isAnagram2()  method gives solution in time complexity of O(n)

     

}

public static boolean isAnagram1(String s1, String s2) {

if (s1 == null || s2 == null )

return false;

int len = s1.length();

if (len != s2.length() || len < 2)

return false;

char[] s1CharArr = s1.toLowerCase().toCharArray();

char[] s2CharArr = s2.toLowerCase().toCharArray();

Arrays.sort(s1CharArr);

Arrays.sort(s2CharArr);

return new String(s1CharArr).equals(new String(s2CharArr));

}

public static boolean isAnagram2(String s1, String s2) {

if (s1 == null || s2 == null )

return false;

int len = s1.length();

if (len != s2.length() || len < 2)

return false;

final int LETTERS_LEN = 256;

int[] letters = new int[LETTERS_LEN];

for (int i = 0; i < len; i++) {

letters[s1.charAt(i)]++;//incrementing the character count

letters[s2.charAt(i)]--;//decrementing the character count

}

for (int i = 0; i < LETTERS_LEN; i++) {

if (letters[i] != 0) {

return false; //returning from first non zero element finding means count mismatch

}

}

return true;

}

}

Output : 

true

true

                 

Pythagorean Triplets

A Pythagorean triple consists of three positive integers a, b, and c, such that a2 + b2 = c2. Such a triple is commonly written (a, b, c), and a well-known example is (3, 4, 5). If (a, b, c) is a Pythagorean triple, then so is (ka, kb, kc) for any positive integer k. A primitive Pythagorean triple is one in which a, b and c are coprime. A right triangle whose sides form a Pythagorean triple is called a Pythagorean triangle.

Finding all the triplets  for c2<= n :

public class PythagoreanTriplet {

        static int count = 0;

public static void main(String[] args) {

Long start = System.currentTimeMillis();

                //time comparison for various number of inputs 

//int n = 100000000;//total time in ms=1118847

//int n = 10000000;//total time in ms=36031

//int n = 1000000;//total time in ms=2122

//int n = 100000;//total time in ms=66

//int n = 10000;//total time in ms=20

//int n = 1000;//total time in ms=2

//int n = 100;//total time in ms=1

int n = 1000;

List<Integer> listOfSquraes = new ArrayList<>();

for (int i = 1;; i++) {

int sqr = i*i;

if(sqr > n){

break;

} else {

listOfSquraes.add(sqr);

}

}

int  k =listOfSquraes.size();

for (int i = 0; i<k; i++) {

findPythagoreanTriplet(listOfSquraes.get(i), listOfSquraes,k);

}

Long end = System.currentTimeMillis();

System.out.println("total triplets found=" + count + " and total time in ms=" + (end-start));

}

public static void findPythagoreanTriplet(int sumRequired,List<Integer> list, int size){

for (int i = 1; i < size; i++) {

for (int j = i+1; j < size; j++) {

int sum  = list.get(i) + list.get(j);

int diff = sumRequired-sum;

if(diff == 0){

count++;

System.out.println("("+(int)Math.sqrt(list.get(i)) + "," + (int)Math.sqrt(list.get(j)) + "," + (int)Math.sqrt(sumRequired)+")");

}

}

}

}

}

Output : 

(3,4,5)

(6,8,10)

(5,12,13)

(9,12,15)

(8,15,17)

(12,16,20)

(7,24,25)

(15,20,25)

(10,24,26)

(20,21,29)

(18,24,30)

total triplets found=11 and total time in ms=2

Time complexity though O(n3) which we can reduce with the improving the search to O(nlogn) , so overall complexity would reduce to O(n2logn).

Installing MongoDB on MacOS X

MongoDB Version : 3.0.7

Mac OS X Version : 10.10.4

Following are step by step installation of the mongodb on the Mac OS :

Start with the Terminal 1 :

1. Get the latest MongoDB from the downloads MongoDB

2. Go to Downloads folder  -- >  cd ~ Downloads/

3.  sudo mv mongodb-osx-x86_64-3.0.7.tgz  /Users/sachin/Documents/software/mongodb [cd ~ is /Users/sachin ]

4. cd ~ Documents/software/mongodb

5. tar xzf mongodb-osx-x86_64-3.0.7.tgz

6. By default MongoDB stores the data  in the /data/db folder , so  we require to create the data and to provide proper permission to it :

  a) sudo mkdir -p /data/db
  b) whoami
      sachin
  c) sudo chown sachin /data/db

7. Adding mongo db to $PATH  : 
  a)  cd ~
  b) pwd 
      /Users/sachin
 c)  vim .bash_profile
 d) export PATH=$PATH:/Users/sachin/Documents/software/mongodb/mongodb-osx-x86_64-3.0.7/bin

8) Starting the MongoDB :

a) Go to new Terminal 2
b) mongod    (it starts the mongo service)

9) Go to Terminal 3 :
a) mongo

MongoDB shell version: 3.0.7

connecting to: test

An Alternate to manually starting the mongoDB using the background job as following : 

10 ) Auto starting the Mongodb  using job : 

a)  sudo vim /Library/LaunchDaemons/mongodb.plist

b)  insert the following text and save the file : 

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN"

  "http://www.apple.com/DTDs/PropertyList-1.0.dtd">

<plist version="1.0">

<dict>

  <key>Label</key>

  <string>mongodb</string>

  <key>ProgramArguments</key>

  <array>

    <string>/Users/sachin/Documents/software/mongodb/mongodb-osx-x86_64-3.0.7/bin/mongod</string>

  </array>

  <key>RunAtLoad</key>

  <true/>

  <key>KeepAlive</key>

  <true/>

  <key>WorkingDirectory</key>

  <string>/usr/local/mongodb</string>

  <key>StandardErrorPath</key>

  <string>/var/log/mongodb/error.log</string>

  <key>StandardOutPath</key>

  <string>/var/log/mongodb/output.log</string>

</dict>

</plist>

c) Load the above mentioned job in the background :

sudo launchctl load /Library/LaunchDaemons/mongodb.plist

Welcome and Enjoy the MongoDB world !!!!!

Generating multiple log file using log4j

It is a good practise to separate out the application log and error log for your application. With a distinguish error logs , monitoring of the project becomes easy and debugging process becomes easy.

Usually in application log, we write many useful information depending upon what the default logging level is set. 

With the latest development in Log4J , the set of built-in levels includes TRACE, DEBUG, INFO, WARN, ERROR, and FATAL. 

If you want to create two different files , one for application and one for errors log, following configuration is required to add in the log4j.properties file kept in the classpath : 

----------------------------------------------------------

# Root logger option

log4j.rootLogger=INFO, app, error

# application log file

log4j.appender.app=org.apache.log4j.RollingFileAppender

log4j.appender.app.File=${catalina.home}/logs/application.log

log4j.appender.app.MaxFileSize=10MB

log4j.appender.app.MaxBackupIndex=10

log4j.appender.app.layout=org.apache.log4j.PatternLayout

log4j.appender.app.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c:%L - %m%n

#error logs

log4j.appender.error=org.apache.log4j.RollingFileAppender

log4j.appender.error.File=${catalina.home}/logs/error.log

log4j.appender.error.MaxFileSize=10MB

log4j.appender.error.MaxBackupIndex=10

log4j.appender.error.layout=org.apache.log4j.PatternLayout

log4j.appender.error.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c:%L - %m%n

log4j.appender.error.Threshold=ERROR

-----------------------------------------------------

File path is used here is the default set value of the tomcat catalina home , if you are using some other application server , then you can use the ${SERVER_HOME} path  or whatever the path , you would like to add.

Above configuration generates two files : 

1 . application.log which contains all the logging information  of INFO and upper level  of logging levels.

2. error.log file only contains ERROR logging level information, so whatever you want keep in the error logs .

Java is Pass by Value or Pass by Reference !!!!

In the Java , there is no concept of pointers and objects are  stated to have passed by value. In case of primitives only values can be passed to a method and in case of java objects , it is said to be pass by reference value.

I think correct term should be termed as  Pass by reference value instead of Pass by Value.

Behind the scene its the passing of the value of the reference bit by bit in the method  so its not passing the reference. Following example would validate the  above facts  :


public class Name
{
String name;

Name(String name){
this.name = name;
}

public static void changeNameReference(Name oldname){
oldname = new Name("John");
}
public static void modifyNameReference(Name oldname){
oldname.name = "Brock";
}

public static void main (String[] args) throws java.lang.Exception
{
Name newname = new Name("Rock");
System.out.println("#1.Original name= " + newname.name + " and system hashcode=" + System.identityHashCode(newname));
changeNameReference(newname);
System.out.println("#2.After changeNameReference method call name= " + newname.name + " and system hashcode=" + System.identityHashCode(newname));
modifyNameReference(newname);
System.out.println("#3.After modifyNameReference method call name= " + newname.name + " and system hashcode=" + System.identityHashCode(newname));

}

}

Output : 
-----------------------------------------------------------------------
#1.Original name= Rock and system hashcode=582216281
#2.After changeNameReference method call name= Rock and system hashcode=582216281
#3.After modifyNameReference method call name= Brock and system hashcode=582216281

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Following points by points to keep understand the above example :

1. Note the Point#1 and # 2 having the same value of the object even though object is passed into the method changeNameReference   which assigning the new reference to the object but original object remain intact.

2. In the point#3 , when a new value is assigned to the  argument object to the method  modifyNameReference , its changed the value of the original object with the  new value "Brock"

3. Value of the object is being passed bit by bit but reference remain same in the Heap memory

4. Note the system hash code value  they are same, so object reference is same  in the heap memory.If reference would have passed then definitely the value system hashcode  would have changed.

Note that Class instance and Array  are the objects in java, so passing the reference value in any method would not affect the reference of the object.

Palindrome

A palindrome is a word, phrase, number, or other sequence of characters which reads the same backward or forward. Allowances may be made for adjustments to capital letters, punctuation, and word dividers. Famous examples include "A man, a plan, a canal, Panama!", "Amor, Roma", "race car", "stack cats", "step on no pets", "taco cat", "put it up", "Was it a car or a cat I saw?" and "No 'x' in Nixon"

Java code to validate the Palindrome is as follow : 

/*

 * @sachin

 */

public class Palindrome {

public static boolean isPalindrome(String input) throws Exception{

if(input == null || input.isEmpty()) {

throw new Exception("Invalid input");

}

String str = input.replaceAll("[^a-zA-Z0-9]", "").toLowerCase();

boolean isPalindrome = true;

int i = 0;

int j = str.length();

for(i=0; i< j;i++){

if(str.charAt(i) == str.charAt(j-1)){

j--;

continue;

} else {

isPalindrome = false;

}

}

return isPalindrome;

}

public static void main(String[] args) {

try {

System.out.println("isValidPalindrome=" + isPalindrome("No 'x' in Nixon"));

                        System.out.println("isValidPalindrome=" + isPalindrome("12321"));

                        System.out.println("isValidPalindrome=" + isPalindrome("sachin"));

} catch (Exception e) {

e.printStackTrace();

}

}

}

Output : 

true

true

false