Hery  LaB

Hery LaB


How to Create Your First Blockchain with Java Code

We’ve all seen how big Bitcoin and other cryptocurrencies have become. While this type of online currency is notoriously volatile, the technology behind it has the potential to disrupt every industry from the inside out. Because blockchain has an endless application scope, it’s being seen in new ways every day.

In this post, we’ll go into the architecture behind blockchain and how a distributed ledger works. Once you see it for yourself, you’ll see why so many developers are embracing blockchain as a new normal. We’ll also dive into a short tutorial for how to create your own (basic) blockchain sequence and use a proof of work (mining) system.

Understanding Blockchain

First, we all need to be on the same page about what blockchain is and how it works before we attempt it ourselves. The block has header information, and there is also a set or a “block” of data. This data is usually a transaction in the world of cryptocurrency, but it can be adapted. The chain then starts with a Genesis block, and new blocks are created depending on just how many transactions or sets of data are stored within a block.

Once that threshold is reached, a new block is created. This new one is linked to the previous one, and that’s where the term blockchain comes from. Blockchains are also immutable. This is because a SHA-256 hash is involved with every transaction or set of data. The content within the blocks is also hashed. This means there’s a unique identifier for every block, and the hash from the linked blocks are stored and hashed in the header as well.

Because blockchains are immutable, they’re incredibly secure. Messing with one is basically impossible. Trying to fake transaction data or property would be a challenge. Even more so, as the chain grows, it gets even more secure. The technology to disrupt this system just doesn’t exist yet, and that’s good news.

There are three types of blockchain:

  • Public –** Public blockchain is one that’s open for anyone to see. The transactions and data all appear on the ledger, and that means everyone can participate in the consensus process.**
  • Federated – Contrary to a public blockchain, federated does not allow everyone to be a part of the consensus process. Instead, there are a limited number of nodes with permission to access the ledger.
  • Private – Finally, private blockchains are mainly used inside companies. These are restricted to only specific members who can access the blockchain and carry out transactions.


Next, let’s talk about transactions within blockchain. Blockchain technology is distributed. Because they’re append-only, it’s easy to duplicate blockchains across nodes in the network. While nodes usually communicate peer-to-peer (like with Bitcoin), they can also be decentralized with APIs via HTTP.

A transaction can be anything. It could have an execution code or just store information. You can see this technology in action with the introduction of new smart contracts. Essentially, these smart contracts are computer protocols which facilitate and verify digital contracts. They’ll likely become more mainstream in industries like manufacturing, banking, and so on.

Let’s look at Bitcoin as an example. With Bitcoin, there is a transaction with a certain amount that is transferred from an owner account into another account. This transaction has public keys and account IDs to make sure it’s secure. These transactions are added to a network, and they’re pooled together. Though they’re in a shared network, they’re not in a block or within the chain itself.

How does this work? It comes down to the Consensus Mechanism. You probably already know of one such mechanism known as Mining, which is used by Bitcoin. There’s an endless list of Consensus Mechanisms and it would take too long to list them all. All you need to know is that they’re algorithms or patterns that gather transactions, build a block and add these blocks to the chain to validate.

Getting Started

As you read above, a blockchain is a chain or list of blocks. Each block comes with its own digital signature as well as the digital signature of the blocks before it. Some might also contain data like transaction information. The digital signature is known as a hash. Each block’s own hash is calculated from the previous one. One change will affect all of the hashes thereafter. By calculating and comparing these, we can see if a blockchain is valid.

Because any changes in data will result in a broken chain, let’s first create a class Block that will form the foundation for the blockchain.

#java #bitcoin #blockchain #cryptocurrency

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How to Create Your First Blockchain with Java Code
Samanta  Moore

Samanta Moore


Guidelines for Java Code Reviews

Get a jump-start on your next code review session with this list.

Having another pair of eyes scan your code is always useful and helps you spot mistakes before you break production. You need not be an expert to review someone’s code. Some experience with the programming language and a review checklist should help you get started. We’ve put together a list of things you should keep in mind when you’re reviewing Java code. Read on!

1. Follow Java Code Conventions

2. Replace Imperative Code With Lambdas and Streams

3. Beware of the NullPointerException

4. Directly Assigning References From Client Code to a Field

5. Handle Exceptions With Care

#java #code quality #java tutorial #code analysis #code reviews #code review tips #code analysis tools #java tutorial for beginners #java code review

Tyrique  Littel

Tyrique Littel


How to Install OpenJDK 11 on CentOS 8

What is OpenJDK?

OpenJDk or Open Java Development Kit is a free, open-source framework of the Java Platform, Standard Edition (or Java SE). It contains the virtual machine, the Java Class Library, and the Java compiler. The difference between the Oracle OpenJDK and Oracle JDK is that OpenJDK is a source code reference point for the open-source model. Simultaneously, the Oracle JDK is a continuation or advanced model of the OpenJDK, which is not open source and requires a license to use.

In this article, we will be installing OpenJDK on Centos 8.

#tutorials #alternatives #centos #centos 8 #configuration #dnf #frameworks #java #java development kit #java ee #java environment variables #java framework #java jdk #java jre #java platform #java sdk #java se #jdk #jre #open java development kit #open source #openjdk #openjdk 11 #openjdk 8 #openjdk runtime environment

Samanta  Moore

Samanta Moore


12 Common Java Mistakes Made by Newcomers

Everyone makes mistakes, not just beginners, but even professionals. This article goes over a dozen common mistakes that Java newbies and newcomers make and how to avoid them. Have you or your colleagues made any of these common Java mistakes early in your career?

Everyone makes mistakes, not only learners or beginners but professionals. As a programming course, the CodeGym team often collects mistakes of newbies to improve our auto validator. This time we decided to interview experienced programmers about mistakes in Java they made closer to their careers start or noticed them among their young colleagues.

We collected their answers and compiled this list of dozen popular mistakes Java beginners make. The order of errors is random and does not carry any special meaning.

#java #learn-java #java-programming #beginners #beginners-to-coding #learning-to-code #learn-to-code #learn-to-code-java

Samanta  Moore

Samanta Moore


Going Beyond Java 8: Local Variable Type Inference (var) - DZone Java

According to some surveys, such as JetBrains’s great survey, Java 8 is currently the most used version of Java, despite being a 2014 release.

What you are reading is one in a series of articles titled ‘Going beyond Java 8,’ inspired by the contents of my book, Java for Aliens. These articles will guide you step-by-step through the most important features introduced to the language, starting from version 9. The aim is to make you aware of how important it is to move forward from Java 8, explaining the enormous advantages that the latest versions of the language offer.

In this article, we will talk about the most important new feature introduced with Java 10. Officially called local variable type inference, this feature is better known as the **introduction of the word **var. Despite the complicated name, it is actually quite a simple feature to use. However, some observations need to be made before we can see the impact that the introduction of the word var has on other pre-existing characteristics.

#java #java 11 #java 10 #java 12 #var #java 14 #java 13 #java 15 #verbosity

Joseph  Murray

Joseph Murray


Minimum Java Knowledge Requirements for Your First Coding Job

What does a potential Java junior need to know to get their first job or even qualify for a trainee position in a good company? What tools will help a Java programmer reach the next level? Which technologies should you study, and which ones are better to hold off on?

There is no standard answer to these questions, just as there is no single action plan that would suit absolutely everyone. Some companies are striving for development, constantly introducing new technologies and testing the capabilities of new versions of the language, while others stubbornly cling to old ones. There are also middle options, and perhaps these are most of them.

I get asked this question so often that I decided to write an article that I can then refer to in order to answer it. In addition, it will be useful not only to those who ask me personally but also to everyone who has already decided (or did not decide in any way) to connect their lives with Java programming.

#java #java-development-resources #java-development #learn-to-code #learning-to-code #beginners #tutorial-for-beginners #beginners-to-coding