Hire the Top 3% of Freelance Java Developers

Demand for Java Developers Continues to Expand

The need for Java developers has been steady for years. Java currently ranks as the seventh most popular technology according to StackOverflow’s 2023 Developer Survey, and its features and performance continue to improve and expand.

Because Java is applicable in many fields, offers a robust development environment and tooling, and boasts an abundance of open-source projects, demand for Java developers will remain strong for the foreseeable future. In fact, according to Zippia, the demand for Java developers in the US market is expected to increase by 13% from 2018 to 2028.

However, hiring Java developers who will be an ideal fit for your needs is not always easy. What technical skills and personal traits should you prioritize? How can you distinguish the best Java developers from others? Does your software development team need an experienced Java programmer, or will a junior candidate be a better fit? This hiring guide provides the context to answer those questions and explains how to hire Java developers capable of meeting your needs.

What Attributes Distinguish Quality Java Developers From Others?

Narrowing your search for Java talent can be challenging due to the technology’s popularity and use across industries. Before progressing to project-specific skills, it is necessary to gauge candidates’ proficiency in essential technical skills, complementary technology skills, and relevant soft skills.

Core Technical Skills for Java Developers

Core Java fundamentals – A good developer has a deep understanding of Java’s basic constructs, namely classes, loops, objects, data types, and so on. Knowledge of more advanced concepts, like generic types, lambda expressions, and Java streams, can help a developer write modern, clean code that can be easily understood by other software engineers on your team. The higher the code quality, the lower the chance of introducing a bug when an application is expanded later in the development process.

Java frameworks and libraries – Dedicated Java developers should have in-depth knowledge of tools like Spring, Hibernate, Jakarta EE, Jackson, and JUnit. Frameworks and libraries like these allow developers to create applications faster, as they free software engineers from writing boilerplate code. They can also help integrate an application with external tools like databases. Most proficient developers can learn to use a new framework or library in a reasonable amount of time. However, when hiring Java developers, it is preferable to select candidates familiar with the libraries and frameworks your team is already using.

JVM internals – A good understanding of the Java Virtual Machine (JVM), especially memory management, helps software engineers write applications that use allocated memory efficiently. Experienced programmers should be able to analyze memory usage, allowing them to diagnose and solve memory-related problems.

Concurrency and multithreading – Familiarity with Java’s concurrent programming tools and techniques allows programmers to write efficient programs that will take advantage of multicore CPUs. A programmer should be familiar with Java threads, locks and synchronization, atomic operations, and asynchronous task calling (blocking versus nonblocking). While virtually all modern CPUs have multiple cores, server processors often feature dozens of physical and logical cores, making multithreading optimization a priority if your in-house team is working on enterprise-grade cloud applications.

Complementary Technology Skills

To develop secure, functional, and high-quality applications, a Java developer may need to use a number of complementary tech skills. These are not necessarily Java skills, but they are tied to technologies closely connected to Java development, and their relevance varies depending on your software development project’s technical requirements:

Security – A highly skilled Java engineer must be familiar with common authentication mechanisms, including the basics of public key infrastructure (PKI) and cryptography (e.g., message digests, symmetric and asymmetric ciphers). They should also know when and how security measures should be implemented. Depending on your industry, the candidate’s level of experience in industry-standard security could play a major role in hiring, especially in highly regulated industries such as finance.

Design patterns – Top Java developers should understand and use common design patterns like Singleton and Factory. Design patterns are tried and tested solutions to repetitive problems. In addition to helping speed up development, they also define a common language that helps your team communicate and collaborate more efficiently.

Database integration – Most applications store user data in databases, so the ability to integrate Java applications with relational (e.g., MySQL, PostgreSQL) and NoSQL databases (e.g., MongoDB, DynamoDB) can be of great importance. If possible, prioritize hiring talent familiar with the databases your team is using or planning to use.

Unit testing and debugging – Every developer makes mistakes, but unit tests can make it easier to spot them early on, effectively acting as the first level of quality assurance. Moreover, unit tests support writing clean code, which is essential for efficient collaboration. For example, if a programmer is struggling to write a unit test for a given method, this may indicate that the method requires refactoring. Developers should be familiar with tools like JUnit to write, debug, and execute unit tests.

Build tools and CI/CD – Many Java developers have ample experience with build automation tools such as Maven and Gradle, and continuous integration/continuous delivery (CI/CD) automation tools such as Jenkins. Though larger teams usually have a dedicated DevOps specialist who takes care of CI/CD, it is essential that a Java developer be familiar with at least Gradle and Maven.

Relevant Soft Skills

Technical skills can be improved as needed, but if you want your team to be productive and cohesive, soft skills are equally important. Java developers typically collaborate with other developers, DevOps experts, testers, and even end users. It is essential to hire Java programmers with good communication skills, a track record of successful collaboration, and a willingness to share their knowledge. You should also consider a developer’s problem-solving and project management abilities.

Furthermore, all software engineers need to continuously improve and refresh their skills. The industry is constantly evolving, with new versions of Java and new frameworks introduced regularly. Adaptability should not be confused with adopting the latest, often unproven, technologies simply because they are new. Make sure the candidate is improving skills that are relevant to your project.

How Can You Identify the Ideal Java Developer for You?

You will need to identify a candidate whose skills and experience match your specific needs and business goals. Do you need a senior Java developer, or will a junior developer be able to fill the role? Do you require an individual with niche-specific expertise or a generalist?

All Java developers should possess core programming skills and a good understanding of Java fundamentals and best practices, but they will specialize in different areas based on various Java use cases:

Back ends – Java is suitable for back-end development and its various tasks, ranging from fairly common APIs (application programming interfaces) that allow mobile or web applications to collect and modify data to complex data processing or streaming tools often deployed in the cloud. Back-end architecture varies, and you may want a candidate focused on monolithic, microservices, or serverless application development.

Mobile apps – Many of the several million Android apps available in the Google Play Store are written in Java, as Java is still an option for native development on Android. Java boasts a mature ecosystem, libraries, frameworks and tools, robust community support, and security features that help developers create modern and secure mobile applications. If you’re looking for Java mobile developers, you likely need talent to update or maintain legacy apps, and you should target candidates with hands-on experience with older applications.

Desktop apps – Desktop applications run on personal computers without an internet browser, and they come with their own user interface and functionalities. There are a number of Java frameworks, such as Swing and JavaFX, that provide a set of components (e.g., frames, buttons, trees, lists) for developers to easily build UI for desktop applications.

Web apps – Web applications run on servers, and users communicate with them via a web browser. A number of popular Java frameworks are available (e.g., Spring MVC, Spring Boot), and in combination with HTML, CSS, and other frameworks, they can be used to create powerful and visually appealing web applications. If you are looking for web app developers, make sure they are familiar with the frameworks your team is using. Additional front-end or UI experience is welcome.

In addition to these common use cases, Java can also be used to create applications for embedded systems, games, big data applications, and other specific software development projects. Hiring Java experts for certain types of projects, such as optimizing an antiquated game engine for performance on multithreaded processors and new generations of GPUs, tends to be more challenging than finding talent for enterprise or mobile app development. You should prepare to allocate more time to the hiring process when searching for these types of specialists, as they are in limited supply.

Java Developers vs. TypeScript, Python, and PHP Developers: Which Engineer Is Best for Your Next Project?

Java, TypeScript, Python, and PHP engineers work across front- and back-end development. All of these popular programming languages have thriving communities with good support and documentation. They are sound choices for different use cases, and Java developers, in particular, excel at building enterprise solutions.

TypeScript developers primarily work on web application front ends, combining TypeScript with popular technologies like Node.js or Angular. TypeScript is today’s fastest growing programming language; it is based on JavaScript but adds new capabilities that make it more robust (such as static type definition). As an increasing number of JavaScript developers embrace and learn TypeScript, sourcing TypeScript talent should not be a problem.

Python developers commonly work on big data, machine learning, DevOps, and web development projects. Python’s frameworks allow developers to create a web application quickly, making it a good choice if the aim is to test ideas, build prototypes, or develop a proof of concept. There is no shortage of Python talent for hire, especially if you are looking for generalists. However, Python developers specializing in certain fields (e.g., machine learning engineers or data science specialists) can be in short supply and command higher rates.

PHP developers are a viable option for a variety of web projects, ranging from custom WordPress development to enterprise web applications. Clients can tap into a large pool of experienced PHP talent when hiring, as PHP is the most popular server-side programming language and is relatively easy to learn.

Java developers are excellent for developing enterprise solutions and certain types of mobile and desktop applications; for projects in which security and performance are priorities, Java surpasses TypeScript, Python, and PHP. But because Java has a steeper learning curve than these languages, it is important to balance a team with both junior and senior Java developers. Fortunately, thanks to its maturity and popularity, you can expect to find a lot of Java talent on the market, including full-stack developers with decades of experience.

Skill Levels and Selection Criteria

When looking for a dedicated Java developer, you should determine whether a junior, mid-level, or senior talent would be the right fit for your project. This decision depends on several factors, such as:

Budget constraints – The broader and more diverse their experience, the higher a developer’s hourly rate will be. When a project’s budget is limited, a junior or mid-level developer might be your only option. However, experienced developers are usually more productive, make fewer errors, and can find viable solutions faster. For this reason, if the project is moderately or highly complex, hiring senior talent could prove more cost-effective than contracting a junior or a mid-level developer. Due to Java’s age, there is an abundance of experienced talent on the market, and pricing tends to be competitive, providing companies with more choice and value.

Complexity of tasks – Even developers with limited experience should be able to tackle simple or moderately complicated problems. Senior developers are better at architecting applications and identifying and solving complex problems (e.g., performance issues). Developers with greater experience are also better suited to choose a technology stack for a given application development project.

Team composition – High-performing teams consist of people with diverse skill sets, experience levels, and perspectives that complement each other. It is not a good idea to create a team that would include only junior developers since they often need guidance and supervision. On the other hand, a junior developer might bring a fresh perspective and extra vigor to a team of senior developers immersed in their routines. The same is true for freelance Java developers who may have worked for dozens of clients, gathering useful experience along the way. This might not matter if your team is focused on a single project (e.g., developing and maintaining an enterprise CRM application), but a diverse team can add value if your company doesn’t specialize in a single type of product.

Here are some basic guidelines for hiring at different skill levels:

Junior developers typically have less than two years of experience, and many are recent graduates or self-taught developers. These programmers are familiar with Java basics and may even have experience working with certain frameworks. However, because they do not have much experience in coding production-grade applications, their work should be limited to simple modules and the resulting code should be reviewed often by more experienced peers.

Mid-level developers usually have up to five years of experience and can work on tasks individually or in a small team. A mid-level developer can solve most technical problems on their own and implement a module based on user requirements. They write clean Java code and have the ability to adapt to an existing codebase and add new features to an application developed by someone else. Mid-level developers are often expected to help junior developers in more demanding tasks.

Senior developers have more than five years of Java experience and can work on more than one problem at the same time. A senior Java developer is capable of making strategic decisions in a project, such as choosing a technology stack or devising an application’s architecture. Senior developers can also act as technical team leaders, assigning and delegating tasks to other team members and checking the quality of their work throughout the development process, whether following the waterfall model of project management or the Agile methodology.

Some candidates possess certificates issued by renowned institutions or companies, such as Oracle’s Java EE and SE certificates, VMware certificates, and so on. Certificates are a useful way to gauge a developer’s proficiency in a specific programming language or technology. However, the ideal candidates will combine a relevant certificate with practical, real-world experience.

How to Write a Java Developer Job Description for Your Project

Start by introducing your company, projects, clients, and products. You can also mention other factors that make your company an attractive employer, such as benefits and advancement opportunities.

Specify the nature of the engagement: Are you looking to hire freelance Java developers for a single project or do you seek a candidate to fill a full-time role on a Java development team? Is the job on-site, remote, or hybrid? Include information about salary ranges, as well.

Outline the project requirements and skills gap you’re seeking to fill before proceeding to list the Java skills mandatory for the job. Follow up with complementary skills you would appreciate in a candidate. Be as specific and thorough as possible in describing the development services you seek. Due to Java’s popularity and use in various fields and industries, a good Java job description needs to include detailed information that will allow potential candidates to self-assess and decide whether or not they should apply. Broad requirements may attract a lot of Java talent but leave you with candidates who lack relevant experience.

You can consult this sample Java Developer job description for more information.

What Are the Most Important Java Developer Interview Questions?

Due to Java’s use in many fields, crafting truly useful interview questions can prove challenging for hiring managers who may be unfamiliar with the programming language’s ins, outs, and industry-specific applications. While there is no shortage of sample interview questions online that you can use for inspiration, remember to tailor your interview questions to your specific requirements.

Consult your software development team, identify the skills you would like to prioritize, and avoid basing the interview on questions that are likely to lead to uninformative, canned responses. The effort invested in tailoring a set of effective interview questions is worthwhile, as specific queries will elicit a much better picture of each interviewee’s aptitude than generic questions will.

What are the main features of Java?

You should start your interview with this basic question, which will give you a quick and high-level overview of the candidate’s understanding of Java. You can then follow up with more specific questions about certain Java programming language features to get a better idea of each candidate’s skill level.

Each candidate’s answer should cover the basics: Java is a class-based object-oriented programming (OOP) language, meaning that Java programs consist of classes that are blueprints for objects. These objects can have fields that store data and methods that are actions that the object is able to perform. Java is famous for being platform-independent. Source code is compiled to bytecode, and then it can be executed on many different operating systems and devices where the JVM is installed. In contrast to languages like C/C++, Java programmers needn’t worry about allocating and deallocating memory. Memory is managed by the JVM, and objects are removed from memory by the garbage collector once they’re no longer needed.

Java provides a rich set of libraries that can be used for I/O operations, cryptography, mathematical operations, and managing networks, connections and sockets. To thoroughly vet applicants, you should prepare additional questions about libraries relevant to your project.

Describe the purpose of using the following design patterns: Singleton, Observer, and Chain of Responsibility.

Knowing design patterns not only helps developers write quality code, but it is also crucial for understanding multiple frameworks that often implement these patterns in the development process. It would be difficult to check if a candidate knows all design patterns in an interview, but asking them to describe several different patterns provides insight into their experience and technical knowledge.

The candidate should be able to describe the patterns and provide examples of when to use them:

• Singleton (a creational pattern) ensures that only one instance of a given class is created. It can be useful in scenarios where multiple instances would lead to conflicts, inconsistencies, or a waste of resources.

• Observer (a behavioral pattern) helps to maintain consistency between multiple components or to notify interested parties when specific events occur. An example of when to use this design pattern might be in a radiator system that “observes” a thermometer: When the temperature falls below a given threshold, the radiator system starts heating to raise the temperature.

• Chain of Responsibility (a structural pattern) recommends splitting data processing into a number of handlers. Each handler has its own logic, and when it is done processing data, it can pass data to the next handler in a chain for further processing. This pattern is used when it’s necessary to execute multiple handlers in a particular order.

Proceed to ask more specific questions. Which pattern would the candidate use in a real-world scenario pertaining to the project? What are their thoughts about using one design pattern over another in a specific scenario?

What are Java Streams, and what can they be used for?

The Java Streams API allows developers to write efficient and concise code for data processing. Use this question to assess the candidate’s understanding of streams and their experience in bulk data operations. The candidate should be able to outline what a stream is and how it is used, and provide a practical example.

A stream should consist of three parts: a source, an intermediate operation or operations, and a terminal operation. There are many ways to create a stream. The source of a stream can be a collection, array, or text file. Once a source is declared, the developer can call intermediate operations like filtering, mapping, or sorting. Intermediate operations can be chained together if more of them are needed to achieve a goal. At the end, a terminal operation should be called, e.g., a stream can collect all processed elements or count them. To improve performance, a developer can execute a stream in parallel mode.

Suppose the developer is working on an application that gives all employees an additional day of vacation if they’ve been with the company more than 10 years. The Java Streams API makes this relatively easy and straightforward. First, a developer would read a list of all employees from a database to a stream. Then, the stream would filter employees who have been working for more than 10 years (based on a specified date). In the next operation, it would increase the number of vacation days by one. In the last (terminal) step, the stream would collect modified employees back to a new collection that could be saved back to a database.

How can Java code be tested?

This seemingly simple question will help you evaluate the candidate’s knowledge of testing tools, automated testing, and test-driven development (TDD).

The candidate’s answer should cover common approaches to testing, such as unit, integration, end-to-end, security, and load testing. The candidate should be familiar with relevant tools for different tests, such as JUnit and TestNG for unit tests. These frameworks help developers verify whether a method behaves as expected when provided with a given input. After unit tests, the implementation of integration tests checks how different components interact with one another. Automated testing in CI/CD pipelines is a good practice and should be mentioned as well.

It’s worth noting that the answer will likely depend on the position they are being interviewed for and the project itself. For example, load-testing expertise is vital for enterprise applications with hundreds or thousands of users, but it won’t be as relevant if the developer is expected to update legacy web and mobile applications with no track record of load or performance issues.

What are the best ways to secure Java RESTful Web Services?

REST APIs are based on URIs and the HTTP protocol and often use JSON for a data format. They’re commonly used and well documented, and this question will test whether or not the candidate has a good understanding of security and authentication.

The answer should include the most popular methods to secure the API:

• Basic authentication is the simplest way to secure the API. The authentication mechanism is based on a username and password that are encoded and passed in a request’s header. Basic authentication is not considered very secure. It can be used for integration with third-party services, but it is not a good choice for securing public APIs.
• Using an API key is another straightforward authentication method. It is well suited for third-party integrations—for instance, a Java web application that needs to show a given address on a map. To obtain the longitude and latitude, the app calls a geocoding API and passes an API key in a request’s header to authenticate itself.
• OAuth2 (with or without JWT) is a common method to secure public APIs and is often used for web applications that communicate with REST APIs. The authentication server verifies a user’s credentials and returns a token that is later appended to all requests sent to the Java application. A token is valid only for a given period of time and may include additional information about a user, e.g., their privileges.

Other popular methods a candidate might mention include a one-time password (OTP), which can be used with SMS verification, and two-factor authentication (2FA), which includes standard credentials verification and a second step, e.g., passing a code from an authentication application installed on the user’s smartphone.

Why Do Companies Hire Java Developers?

Since its introduction in 1995, Java has gone through numerous iterations and enabled the creation of countless applications across different platforms. Considering its age, some may ask, why hire a Java developer at all? Despite its maturity, Java developers still create new, cutting-edge applications that accommodate millions of users, which is perhaps the best testament to Java’s versatility and popularity.

Companies hire Java developers to create a variety of consumer and enterprise applications that run on desktop, mobile, and web platforms. Java is used across many industries, ranging from e-commerce and financial services to social media and entertainment. Given Java’s popularity and the number of knowledgeable developers, startups, SMBs, and enterprise companies can rest assured that an extensive talent pool of Java developers for hire will be available for years to come. This means long-term maintenance should not be an issue, and businesses will be able to find skilled Java developers for future updates and improvements.

The technical content presented in this article was reviewed by Fredrik Håård.