2021 January

What are concurrency problems and how to avoid them in Java

Concurrency problems appear when your code is executed by more than one thread. Then, in contrast to a single-threaded execution, your code might behave differently depending on when and which thread accesses a variable. Here is an example: In the above code: There is a static variable counter starting from 0. A fixed thread pool… read more »

Period, Duration and Instant in Java

Period, Duration and Instant are three different classes introduced since Java 8 to help us deal better with time. Period measures the time with days granularity. In other words, there are no hours, minutes, nor seconds. Example: There are also methods ofDays, ofMonths and so on. It’s noteworthy to mention that you cannot convert automatically… read more »

Why and How to Use Optional in Java

The Optional object type in Java was introduced with version 8 of Java. It is used when we want to express that a value might not be known (yet) or it’s not applicable at this moment. Before Java 8 developers might have been tempted to return a null value in this case. Ultimately, there are… read more »

Introduction to Tengine Web Server

Tengine seems to be a popular web server for Chinese websites. I’ve come upon it while browsing through Aliexpress and stumbling upon a 404 error: This error and more specifically its footer “Powered by Tengine” stirred up my interest and so I started looking for more information about this unknown to me web server. Here… read more »

Why and How to Use Java.util.stream.Collectors

Streams are a wonderful feature in Java allowing you to write clean, efficient and powerful code. If you haven’t consumed the output of the stream, you will probably want to collect it. That’s when the methods from Java.util.stream.Collectors come to help. Here are some useful examples: Collect to list: We start with a list of… read more »

Java Built-In Functional Interfaces Cheatsheet and Examples

In order to use lambda expressions in Java 8, you need a functional interface. For most of your needs, you can use the already built ones in Java which are as follows: Supplier – generate output without taking any input. For example, get the current date: Then use getDate to assign a LocalDate variable: Consumer… read more »

Java Generics With Upper and Lower Bounds Simply Explained

Generics in Java and especially such with upper and lower bounds can be confusing even though they are otherwise very useful. Here is an example which explains it all well: We have two classes – A and B. B extends A. We’ll use them to test the upper and lower bounds of the wildcard generics… read more »

Avoid the Telescoping Anti-pattern in Java

The Telescoping anti-pattern is widely-spread, just like a virus. It starts with good intentions. For example, a class that has two properties like this: The above constructor starts being used for creating new Example objects. At one point, the project requirements change and a third parameter is needed. For example, let’s assume that the above… read more »

How to Create Immutable Objects and Properties in Java

Being able to create an immutable object in Java is one of the most essential skills for any Java programmer. Such objects are needed when you want to rest assured that a created object cannot change for whatever reason. The common approach is to create an object with private final fields and allow only getters… read more »

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