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  So we have 2 thread, one will be printing odd numbers and others will be printing even number. We have to print them in a synchronized fashion.  class Lock {     Boolean isOdd;     Lock(Boolean odd) {         this.isOdd = odd;     }     synchronized void print(Integer number) {         Boolean numberEven = number %2 == 0;         while (isOdd == numberEven) {             try {                 wait();             } catch( InterruptedException e) {                Thread.currentThread().interrupt();             }         }         System.out.println(number);         isOdd = !isOdd;         notify();     } } class PrintThread...

I will try to explain consistent hashing with a real world example. Let's assume I have a restaurant with 60 tables and 5 servers (waiter). Each server is given an equal number of tables to serve. Now let's assume we have addition of a new server (waiter), so his addition will be marked in the circle and he will be receiving tables from the previous server to his distance only. Check the attached example. Assume a server (waiter) has left the organisation and we have only 4 servers now. Server3 has left the restaurant, so his table will be assigned to server 4. I am sure you have noticed the load is not equally distributed. But to make the system less prone to addition/removal we just rotate in clockwise and assign range from the previous server to present server.  To make sure load is balanced or optimally balanced we need to use virtual nodes. Check links here: http://tom-e-white.com/2007/11/consistent-hashing.html https://www.toptal.com/big-data/...

what is immutable class. A class whose object can not be modified. So we have to make sure we have stop all the mechanism which allows user to change the stage. * Member Variable - Make them final so no one can change state. * Class as Final - So derived class can not override the behavior. * No Setter method - So its can not be changed later in case you missed to  initialize in constructor. public Final class DataReceiver { final string port_id; public DataReceiver( String port) this.port_id = port; } public String getPortID() { return port_number; } } Above class will be used as immutable now. :)

We have filled a  cylindrical glas s with water. We have to measure that  glass have exactly 50% of water. We don't have any measuring instrument.  Solution: Two ways can be there. First tilt the glass to the point water reaches to brim of glass. This same point other side water should be exactly at upper bottom. If this happens them you have water half measured. If water is lower than upper bottom then its less than 50% and if more than upper bottom then more than 50% water is there. Other way is to mark the current level of water on glass by placing a finger there.  Cover glass head with you palm or disc and turn over the glass. If water still touches marked location only then its exact half.

A merchant has bough some 3000 banana from market and want to bring them to his home which is 1000 km far from Market. He have a elephant which can carry maximum of 1000/- banana at time. That could have been easy but this elephant is very shrewd and he charges 1 banana for every one kilometer he travel. Now we have to maximise number of banana which should reach to home. Solution: At present we are at 0th km with 3000 banana and elephant. Lets see if elephant have to shift all the 3000 banana and elephant by 1 km. For 1 km shift: Take first 1000 banana and drop at 1st km. 2 banana consumed. One banana each for to and fro. Second  1000 banana and drop at 1st km. 2 banana consumed. Third 1000 banana and reach at 1st km. 1 banana consumed. So all in all total 5 banana will be consumed if we shift a kilometer. But that's not all, our total banana number are also reducing so we may have to reduce the number of turns too. And this will happen once we have reduced the b...

1, 20, 33, 400, 505, 660, 777, 8000, 9009, ........ Seems to be little strange ..huh. Most of times when i see this kind of series and i dont get a clue in couple of minutes, i become so mad with me. Fortunately today i could solve this in minutes. Here is explanation, sequence is Natural Number's binary representation * Number. Number  Binary  Binary * Number 1 1 1 2 10 20 3 11 33 4 100 400 5 101 505 6 110 660 7 111 777 8 1000 8000 9 1001 9009

Elvis operator could have been a good use here. But unfortunately have been decline till now. Its used to say "?." Operate only if not null. Class A {  public B getB() {    return new B(); } } public void test( A a) {     if ( a != null  )         return a.getB();  } Above method would be replaced with public void test ( A a) {      return a?.getB();  } Unfortunately its still some time we can see some think like that. So till that we have to live with two choices: 1. Check for null. 2. Use the Null Object Pattern. So we all know that how to check for null objects and believe me i had real long chain of checking null. Second way can be useful but if this chain is pretty long its can be tiresome to have null object for all the hierarchy Null Object means there will be definition of class A (mostly derived from same interface.) and will have dummy methods which will nullify any ca...