The Bill Pugh Singleton Pattern: An In-Depth Guide What is a Singleton? A singleton is a design pattern used to ensure that a class has only one instance and provides a global point of access to that instance. This pattern is widely used in scenarios where it’s essential to have a single point of control, such as logging, configuration settings, or database connections. Why is Singleton Needed? Singletons are used to: ...
As a developer working with Java on macOS, you might encounter cryptic errors related to Java configuration. One common culprit is an incorrectly set or missing JAVA_HOME environment variable. In this blog post, we’ll explore how to diagnose and fix these issues, ensuring smooth sailing for your Java-based projects. The Problem: “Could not get a real path from Java Home” Picture this: you’re excited to start a new project using Maven Daemon (mvnd), but when you try to run it, you’re greeted with an error message like this: ...
Overview This note covers the concepts of upcasting, downcasting, and serialization in Java. It explains what happens to object fields during these processes and includes a practical example. Classes Definition Let’s define two classes, Alpha and Beta, where Beta is a subclass of Alpha. class Alpha { int a1; int a2; int a3; } class Beta extends Alpha { int b4; } Upcasting When you upcast an object of a subclass (Beta) to its superclass (Alpha), you are changing the reference type but not the actual object in memory. ...
In modern Java development, we often encounter scenarios where we need to prioritize one list over another based on certain conditions. A common approach might involve multiple if-else statements or nested null checks. However, by leveraging the power of Optional and streams, we can achieve this in a more elegant and concise manner. Let’s explore a technique that combines Optional.ofNullable() with streams to create clean, readable code for list prioritization. ...
When working with data collections and databases, maintaining the correct order and efficiently querying your data are crucial. Recently, I faced two common issues: querying for a specific array element in MongoDB and preserving insertion order when converting a stream to a set in Java. Let’s dive into how to solve these problems. Querying for the First Element in a MongoDB Array In MongoDB, you might need to query a document to check if a specific value is the first element in an array. This can be achieved with a simple query, without needing the $elemMatch operator. Here’s how you can do it: ...
When dealing with complex data structures that involves classes and sub-classes in Java that require JSON serialization and deserialization, managing polymorphism can be challenging. Fortunately, the Jackson library provides powerful annotations like @JsonTypeInfo and @JsonSubTypes that simplify this task. Jackson Annotations Jackson’s annotations @JsonTypeInfo and @JsonSubTypes are pivotal for handling polymorphic types. They enable Jackson to serialize subclass types accurately and deserialize JSON back into the correct Java subclasses. @JsonTypeInfo Usage The @JsonTypeInfo annotation helps specify metadata about how subclasses are identified in the JSON output. Key attributes include: ...