Multithreading in Java

A refresher on Multithreading in Java

Multithreading: Runnable vs Thread

Handling Multithreading with Synchronization

Synchronization: Object vs Class level

Understanding Thread Priority

Thread Basics: Sleep, Join and Yield

Understanding wait, notify and notifyAll using producer-consumer problem

ExecutorService

ExecutorService with Callable and Future

Java Collection Framework and Generics

As the name suggests, a Java Collection is a collection of objects represented as a single unit. The idea is to provide a set of operations on the logically grouped elements like searching, sorting, etc.

collection framework hierarchy — source: https://techvidvan.com/tutorials/java-collection-framework/

As the image above shows, there are two core interfaces, Collection and Map. The collection further has interfaces for List, Queue, and Set. For each of these interfaces than we have a concrete set of classes implementing the functionality.

Let’s take a very simple example

Collection values = new ArrayList();
values.add(1);
values.add(2);
values.add("kamal");

We can see collection interface helps us create a new ArrayList, which gives us flexibility over the array where the List can grow during runtime.

But one challenge we can see in the code above is that when we are able to add numbers as well as String to the ArrayList. This is in contrast with the type safety provided by Java. To solve this Java provides us Generics to control over types of elements that can be added to a collection.

Generics Example

class MyClass<T>{
T value;

public T getValue() {
return value;
}

public void setValue(T value) {
this.value = value;
}
}

Coming to our previous code for creating collections

Collection<Integer> values = new ArrayList<>();
values.add(1);

In this example, we cannot add a String to values now.

What if we want to get or add into ArrayList at a particular index. List Interface adds these features on top of Collection. As already depicted in the hierarchy, List inherits Collection and then adds features on top of it.

List<Integer> values = new ArrayList<>();
values.add(1);
int num = values.get(0);

Iterating over a Collection

There are multiple ways to iterate over a collection

List<Integer> values = new ArrayList<>();
values.add(1);
values.add(2);
values.add(3);
Iterator<Integer> i= values.iterator();
while(i.hasNext()) {
    System.out.println(i.next());
}

Another way is to use for loop

for(Integer num:values) {
   System.out.println(num);
}

Or we can use Streams

values.stream().forEach(System.out::println)

Comparable vs Comparator

Another important thing one would like to do with the collection is to arrange elements in sorted order. For example, say we have a List created for Student class objects, and we want to arrange based on Roll numbers.

The easiest way is to make the class implement comparable

class Student implements Comparable<Student>{

 int rollno;
 String name;

 public Student(int rollno, String name) {
  this.rollno=rollno;
  this.name=name;
 }

 @Override
 public int compareTo(Student o) {
  return this.rollno<o.rollno?-1 : (this.rollno==o.rollno)?0:1;
 }
}

// In calling code, we can sort list made up of students 
Collections.sort(list);

There can be cases where it is handy to maintain comparison based on multiple criteria. For example, along with roll number, we want to make sure we can sort the list of students based on names in alphabetical order. In such a case it makes sense to implement Comparator as we can implement multiple comparators based on our need.

class NameComparator implements Comparator<Student>{
 @Override
 public int compare(Student o1, Student o2) {
  return o1.name.compareTo(o2.name);
 }
}

// In calling code, we will send compatator instance 
Collections.sort(list, new NameComparator());

JWT Token

Authentication and authorization are the most important security features to be implemented for any API. One way to manage this information is through sessions. Once users log in, a session is created on the server-side for the user with user metadata information. The problem with this approach is that this is stateful and difficult to scale. Another way to implement the metadata is to send back a hash or a key once the user logs in successfully, and every subsequent request needs to pass this key back. This key is stored along with user metadata is stored in the database to avoid statefulness. The disadvantage here is an additional database query, every time a request comes in.

JWT or JSON Web Token solves this problem. JWT is a string in JSON format, encrypted with a key. The encryption can be symmetric or asymmetric. JWT contains 3 sections, a header, a payload, and a signature.

Header: The header JSON normally contains two fields, a type (typ), which is always “JWT” and alg field providing algorithm used for encrypting the token.

{ "alg": "HS256", "typ": "JWT" }

Payload: This section contains JSON for any payload or data you want to send. This can contain fields that can identify the user and their roles for authorization and authentication. This can also have iat or Issued At time and token expiry time (exp).

{ "sub": "1234567890", "name": "John Doe", "iat": 1516239022 }

Signature: The signature is the encrypted part of the token. The encryption is done using the algorithm mentioned in the header. The signature can only be decrypted using the secret key.

Sample JWT token

Originally posted: https://cloudyforsure.com/security/jwt-token/

4Ps of Marketing

Product

Product Levels

Search Goods: You search and compare characteristics before you buy, for example, in mobile- screen size, camera pixel, features, etc.

Experience Goods: where you can categorize as good or bad after experience only, for example, a stay in a hotel for the first time.

Credence Goods: Where you cannot categorize even after consumption for example an online course (you do not have anything to compare to unless you have taken another course on the subject).

Product Life Cycle or PLC

BCG Matrix

The-Growth-Share-matrix — https://www.smartinsights.com/marketing-planning/marketing-models/use-bcg-matrix/

Promotion

The second P of marketing is Promotion, which is a basic means for generating awareness about the product and create a desire to buy.

6M strategy model

Mission: What is the objective?
Market: Who are my customers?
Message: What I will tell my customers?
Media: How do I reach them?
Money: Budget
Measure: Was the campaign effective?

Two choices of channels

Personal Communication: Mostly more effective and low price via Telemarketing, Emailing or one on one meetings.
Impersonal communication: Mass media via Newspaper or T.V.

Place

The third P of marketing is Place. This gives the convenience of product availability at an arm’s length and helps build trust with customers.

Price

The fourth P of marketing is Price. A fundamental mistake done by companies is to think of price as cost + profit. Ideally one needs to do market research and competitive analysis to come up with the target price. Once one has a target price, it helps to come up with a target cost and help figure out how much to be spent on RnD, marketing, manufacturing, etc.

Two common pricing strategies are skimming (enter high and then move to low) and penetration (enter low and move to high).

price-skimming-vs-penetration-pricing — https://www.economicshelp.org/blog/glossary/penetration-pricing/

Going rate pricing is another strategy where current pricing is studied in the market and an average is taken for pricing the product.

Marketing Basics

In a dictionary Marketing is defined as “the action or business of promoting and selling products or services, including market research and advertising.“.

Before getting into depth, let’s take a step back and refer to the famous question asked in the paper “Marketing Myopia” by Levitt, i.e. “What business are you really in?“. The question forces one to think beyond what products are you selling to what “needs” of customers are you fulfilling. Marketing is all about understanding customer needs.

“Need” is a state of dissatisfaction. Need is a problem and “want” is the solution. I “need” to communicate, I “want” a phone. A “want” combined with a willingness to pay becomes the demand – I am ready to pay for an ‘iPhone”.

Another important aspect is to understand the “value” that the product is adding to the customer. Say, I have the option of buying two phones, I would like to buy the one which gives more value. Perceived value can be thought of as perceived benefits – perceived cost.

P(V) = P(B) – P(C)

While choosing a product over other

P(B1)-P(C1) > P(B2) – P(C2)

or B1-B2 > C1- C2

or Extra Benefits I am getting is more than the extra cost I am paying.

Segmentation – Targeting – Positioning

Segmentation is about grouping your customers by identifying commonalities based on their needs. Segmentation should not be geographical (urban/ rural, north/ south), or demographic (age, sex, education, economic class) but based on personality, values, lifestyle, and behavior.

Segmentation is a three-step process

Clustering
Profiling
Assigning a segment descriptor

Targeting is to select the segments that you will focus on.

There are the following targeting approaches

Mass Market: un-differential
Focus on all, but with the segmented approach: Diffeerential
Focused Strategy: One or two segments

Factors to be considered while targeting

Sales Potential: How much sales can be made for the segment?
Profitability
Consumer Maturity
Competition
Own Abilities

Competition: A less fragmented market can provide healthy competition. HHI or Herfindahl-Hirschman Index can provide a good measure to check how fragmented the market is.

HHI= s1^2 + s2^2 + s3^2 + …sn^2

where: sn=the market share percentage of firm n

0–Bad—-0.2——-0.4—————-Good——————-1

Positioning is “what to tell these customers?” so that they chose you.

While positioning one can take two approaches

Point of Parity or PoP: How are we similar to other products?
1. Category Point of Parity
2. Competitive Point of Parity
Point of Difference PoD: How are we different from other products?

SWOT Analysis

Strength – Weakness – Opportunity – Threat analysis is an old tool used by product teams to understand their characteristics. An important aspect one needs to take care of is all your strengths should map to opportunities, and similarly, weaknesses should map to threats.

5C Analysis

https://svaerm.com/en/blog/situation-analysis/

Branching Strategies

When one starts a project, one question that needs to be answered immediately is how to manage the code? The branching strategy needs to be finalized, in the agile world, we want to make sure code gets merged and deployed asap. Continuous Integration and Continuous delivery want us to make sure our code is always in a state that is ready to be deployed on production.

There are two most common branching strategies which are used in Industry. I have written about these in my book on microservices. Here is an overview.

Feature-Based Branching

The idea is to separate branches for each feature. The feature gets merged back to the production branch once it is implemented and tested completely. An important advantage this kind of approach gives us is that at any point in time there is no unused code in the production branch.

Single Development Branch

In this approach, we maintain a single branch in which we keep on merging even if the feature is incomplete. We need to make sure the half-built feature code is behind some kind of flag mechanism so that it does not get executed unless the feature is complete.

WebSockets

A normal flow between client and server over HTTP connection is made of Requests and Responses.

The client sends a response to the server and then the server sends back the response. Now there can be use cases where the server would have to send data to the client, for example, a chat application or a stock market tracker. In such scenarios, where the server needs to send data to the client at will, WebSocket communication protocol can solve the problem.

WebSocket provides full-duplex communication channels over a single TCP connection. Both HTTP and Websocket protocols are located at layer 7 in the OSI model and depend on TCP at layer 4.

Websocket Connections string looks like ws://some.example.com or for secured wss://some.example.com

To achieve the communication, the WebSocket handshake uses the HTTP Upgrade header to change from the HTTP protocol to the WebSocket protocol.

WebSocket handshake

The client sends a request for “upgrade” as GET 1.1 upgrade
The server responds with 101- Switching protocols

Once the connection is established, the communication is duplex, and both client and server and sent messages over the established connection.

Challenges with Websockets

Proxy is difficult at Layer 7. It will mean 2 levels of WebSocket connectivity, client to proxy and then proxy to backend.
Layer 7 load balancing is difficult due to the stateful nature of communication.
Scaling is tough due to its stateful nature. Moving the connection from one installed backend to another would mean resetting the connection.

Disclaimer: This post was originally posted by me in the cloud community –https://cloudyforsure.com/networking/websockets/

HTTP 1 vs 2 vs 3

For years, the Internet is powered by HTTP protocol helping millions of websites and applications deliver content. Let’s take a look at the journey of the HTTP protocol, its past, present, and future.

HTTP 1

The current version of the HTTP 1 protocol is actually HTTP 1.1. But let’s start with HTTP 1, which was a simple request-response protocol.

HTTP 1.1

As we can see in HTTP 1 implementation, one major problem was that connection needed to be established after each request. To solve this problem HTTP 1.1 came up with a keep-alive concept which helped to send multiple requests over a single connection. To achieve the speed, HTTP1.1 had 6 TCP connections behind the scenes instead of 1.

HTTP 2

Though HTTP 1.1 was much faster than HTTP 1, it had some problems, most importantly, it was not making use of TCP connection completely. Each connection was sending one request at a time. This problem was solved in HTTP 2 and multiple concurrent requests could be sent.

To achieve this parallel request over a single HTTP connection, HTTP 2 uses the concept of streams. That is, each request being sent from the client has a unique stream id attached behind the scenes. This helps the client and server identify the calling and receiving endpoints. One can think of each stream as an independent channel for communication.

HTTP 3

One problem with HTTP 2 is that the streams we have defined are at the HTTP level. TCP is not aware of the concept and is just sending packets at a lower layer. So if there are 4 independent requests sent using 4 different streams, and even if a single packet for any of the requests is lost in the communication, the backend server will keep waiting for the packet and all 4 requests will wait.

HTTP 3 plans to solve this problem by implementing HTTP over QUIC instead of TCP. QUIC too has the concept of streams inbuilt, so in the above-mentioned scenario, when one packet is lost for one request out of 4, only one stream is impacted and response for the other 3 requests will be successfully served.

Disclaimer: This post was originally posted by me in the cloud community –https://cloudyforsure.com/networking/http-1-vs-2-vs-3/

Corporate Finance: Value Maximization

Value Pentagon

Company as-is value is the value of the company without any restructuring or change.

The company’s optimum value is the value that can be achieved after the restructuring is done.

Internal restructuring: Find out redenancies, wastages, remove bottlenecks.

External Restructuring: Merger, demerger, acquisition, etc.

Financial restructuring: Writing down useless assets, debt restructuring etc.

Shareholder vs Stakeholder value

When we talk about the value of the company, they normally have two approaches, increase shareholder value or stakeholder value. Both approaches have their pros and cons. The shareholder value approach is easy to track, as you can look at the numbers and figure out if the shareholder value has increased. But at the same time, this approach can be myopic and focus on short-term goals.

The stakeholder value approach has a broader view, where it talks about customers, employees, society, shareholders, and other stakeholders. The problem here it is hard to track as there is no direct way to track it. For example, giving better discounts and better salaries might help me keep my customers and employees happy, but might add to losses.

Measuring shareholder wealth creation

Market Value Addition or MVA is an important aspect to understand shareholder value. For example, there are two companies, A and B, both with a market cap of say 1000 crore. But the network of company A is 500 crore and company B is 250 crore. We can see MVA for company A is 500 crore whereas company B is 250 crores. In other words, the market view potential for growth in company B.

Corporate Restructuring

Corporate restructuring includes acquisitions, demergers, joint ventures, etc. For example, buying Corus helped Tata steel to jump from 55th ranked in steel revenue worldwide to 5th rank.

Corprate restructuring can be done by

Expansion: Absorption, Tender Offer, Asset acquisition, Joint venture, etc.

Contraction: Demerger – Spin off, split off, split up, Equity carve out etc.

Corporate Control: Going private, Equity buyback, leveraged buyout, etc.

Corporates can unlock value by demergers. Studies report that the observed value of the diversified firm is, on average, 15 percent less than the sum of the implied market value of its divisions, as compared to stand-alone market values of single-segment firms in those industries.

Factors behind diversification discount

Information hypothesis: the inability of markets to correctly evaluate conglomerate structures with unrelated businesses, leading to possible undervaluation.

Inefficient Management hypothesis: the inability of the managers to efficiently manage unrelated businesses.

Inefficient investment hypothesis: distortion of investment due to competition among units for resources.

Modes of asset disposition

Slump sale: Slump sale means the transfer of one or more undertakings as a result of the sale for a lump sum consideration. For example, Ruchi Soya buying biscuit business from Patanjali Natural Biscuits Pvt Ltd (PNBPL) for 60 crores.

Spin-Off: A spinoff is the creation of an independent company through the sale or distribution of new shares of an existing business or division of a parent company. When a new company B is carved out of company A, mostly shareholders of company A will get some proportional shares of company B.

Spin-Off helps in

Unlocking hidden value: establish a public market valuation for undervalued assets.
Undiversification: divest non-core business and sharpen strategic focus
Institutional sponsorship: Promote equity research coverage
Public currency: the public currency for acquisition and stock-based compensation programs
Motivating Management
Eliminating dis-synergies
Corporate Defence: Divest “crown jewel” asset to make the takeover of parent company less attractive.

Challenges in spin-off: There are certain aspects that need to be managed, for example, if the parent company has debt, how this debt will be divided between parent and spin-off company. The lenders need to agree on the arrangement.

Split-Off: In a split-off, the parent company offers its shareholders the opportunity to exchange their parent-co shares. For example, a big shareholder can give up shares in the parent company to gain controlling stakes in the new company.

Split-up: Division of a company into two or more publically traded companies. The difference here is that instead of the parent company and spun-off company, we have completely new companies into existence.

Equity Carve-out: Also known as IPO carve-out, the parent company sells a portion or all of its interests in a subsidiary to the public in an initial public offering.

Financial Restructuring

Cleaning up a balance sheet: writing off losses, writing down useless assets, can be done through asset restructuring and recapitalization.

Debt Restructuring

Strategy-Driven: Restructure debt by lowering the interest rates.
Crisis-Driven: When a company defaults, the company is forced to restructure debt.

Equity Restructuring

Special dividend: One-time dividend
Share buyback: reduces the shareholder base. As a regulatory requirement, the debt-equity ratio should be 2:1, after the buyback. Buyback can happen through the open markets, tender offers, and buyback from employees.
Stock Splits: helps with liquidity
Bonus Shares: When the company is growing fast but does not want to distribute cash in form of a dividend, a bonus share will help reward the shareholders.