Baeldung Pro comes with both absolutely No-Ads as well as finally with Dark Mode, for a clean learning experience:
Once the early-adopter seats are all used, the price will go up and stay at $33/year.
Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.
Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.
To learn more about Java features on Azure Container Apps, visit the documentation page.
You can also ask questions and leave feedback on the Azure Container Apps GitHub page.
Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.
Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.
To learn more about Java features on Azure Container Apps, you can get started over on the documentation page.
And, you can also ask questions and leave feedback on the Azure Container Apps GitHub page.
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.
Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.
With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.
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Mocking is an essential part of unit testing, and the Mockito library makes it easy to write clean and intuitive unit tests for your Java code.
Get started with mocking and improve your application tests using our Mockito guide:
Handling concurrency in an application can be a tricky process with many potential pitfalls. A solid grasp of the fundamentals will go a long way to help minimize these issues.
Get started with understanding multi-threaded applications with our Java Concurrency guide:
Spring 5 added support for reactive programming with the Spring WebFlux module, which has been improved upon ever since. Get started with the Reactor project basics and reactive programming in Spring Boot:
Since its introduction in Java 8, the Stream API has become a staple of Java development. The basic operations like iterating, filtering, mapping sequences of elements are deceptively simple to use.
But these can also be overused and fall into some common pitfalls.
To get a better understanding on how Streams work and how to combine them with other language features, check out our guide to Java Streams:
Explore Spring Boot 3 and Spring 6 in-depth through building a full REST API with the framework:
Yes, Spring Security can be complex, from the more advanced functionality within the Core to the deep OAuth support in the framework.
I built the security material as two full courses - Core and OAuth, to get practical with these more complex scenarios. We explore when and how to use each feature and code through it on the backing project.
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Spring Data JPA is a great way to handle the complexity of JPA with the powerful simplicity of Spring Boot.
Get started with Spring Data JPA through the guided reference course:
End-to-end testing is a very useful method to make sure that your application works as intended. This highlights issues in the overall functionality of the software, that the unit and integration test stages may miss.
Playwright is an easy-to-use, but powerful tool that automates end-to-end testing, and supports all modern browsers and platforms.
When coupled with LambdaTest (an AI-powered cloud-based test execution platform) it can be further scaled to run the Playwright scripts in parallel across 3000+ browser and device combinations:
Yes, we're now running our Spring Sale. All Courses are 25% off until 26th May, 2025:
Yes, we're now running our Spring Sale. All Courses are 25% off until 26th May, 2025:
1. Overview
In this short article, we’ll be looking at an interesting data structure in the Apache Commons Collections library – the BidiMap.
The BidiMap adds a possibility of looking up the key using the corresponding value on top of the standard Map interface.
2. Dependencies
We need to include the following dependency in our project for us to use BidiMap and its implementations. For Maven based projects, we have to add the following dependency to our pom.xml:
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-collections4</artifactId>
<version>4.5.0-M2</version>
</dependency>For Gradle-based projects, we have to add the same artifact to our build.gradle file:
compile 'org.apache.commons:commons-collections4:4.5.0-M2'The latest version of this dependency can be found on Maven Central.
3. Implementations and Instantiation
BidiMap itself is just an interface that defines behaviors unique to a bi-directional map – and there are of course multiple implementations available.
It’s important to understand that implementations of BidiMap do not allow key and value duplicates. When a BidiMap gets inverted, any duplicate values will be converted to duplicate keys and will violate the map contract. A map must always have unique keys.
Let’s look at different concrete implementations of this interface:
- DualHashBidiMap: This implementation uses two HashMap instances to implement the BidiMap internally. It provides fast lookup of entries using either an entry’s key or value. However, two instances of HashMap have to be maintained
- DualLinkedHashBidiMap: This implementation uses two LinkedHashMap instances and consequently maintains the insertion order of map entries. If we don’t need the insert order of the map entries to be maintained, we can just use the less expensive DualHashBidiMap
- TreeBidiMap: This implementation is efficient and is realized by a Red-Black tree implementation. The keys and values of TreeBidiMap are guaranteed to be sorted in ascending order using the natural ordering of the keys and values
- There is also DualTreeBidiMap that uses two instances of TreeMap to achieve the same thing as TreeBidiMap. DualTreeBidiMap is obviously more expensive than TreeBidiMap
The BidiMap interface extends the java.util.Map interface and so can serve as a drop-in replacement for it. We can use the no-arg constructor of the concrete implementations to instantiate a concrete object instance.
4. Unique BidiMap Methods
Now that we’ve explored the different implementations let’s look at methods that are unique to the interface.
The put() inserts a new key-value entry into the map. Note that if the value of the new entry matches the value of any existing entry, the existing entry will be removed in favor of the new entry.
The method returns the removed old entry or null if there’s none:
BidiMap<String, String> map = new DualHashBidiMap<>();
map.put("key1", "value1");
map.put("key2", "value2");
assertEquals(map.size(), 2);The inverseBidiMap() reverses the key-value pair of a BidiMap. This method returns a new BidiMap where the keys have become the values and vice-versa. This operation can be very useful in translation and dictionary applications:
BidiMap<String, String> rMap = map.inverseBidiMap();
assertTrue(rMap.containsKey("value1") && rMap.containsKey("value2"));The removeValue() is used to remove a map entry by specifying a value, instead of a key. This is an addition to Map implementations found in the java.util package:
map.removeValue("value2");
assertFalse(map.containsKey("key2"));We can get the key mapped to a particular value in BidiMap with the getKey(). The method returns null if no key is mapped onto the specified value:
assertEquals(map.getKey("value1"), "key1");5. Conclusion
This quick tutorial provided a look into the Apache Commons Collections library – specifically at BidiMap, its implementations and idiosyncratic methods.
The most exciting and distinguishing feature of BidiMap is its ability to look up and manipulate entries via keys as well as values.
The code backing this article is available on GitHub. Once you're logged in as a Baeldung Pro Member, start learning and coding on the project.
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