How to Evaluate Java Developers' Skills

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Even though dozens of new programming languages have emerged in the 25 years since Java was originally launched in 1995, Java developers still have a high need. Indeed, Java remains one of the most in-demand programming languages on the employment market.

A smart Java developer can create distributed web apps and complex desktop programs that can operate on any platform using the ability of the Java Virtual Machine (JVM) underneath the platform.

According to a survey done by Indeed, Java Developers have the lowest career-switch rate (7.5 percent).

What expertise do Java developers possess?

Data Structures

Because data structures (String, Array, List, Map, Set, Vectors, and Matrix) are the essential building blocks of programming, all developers, regardless of experience level, should have a solid grasp of them.

Design patterns and object-oriented programming

By far, the most popular programming paradigm in the IT industry is OOP. It enables the creation of a program while preserving the structure of things as they exist in real life, making it an excellent tool for modeling and organizing very complex applications.

Design patterns are programming language agnostic approaches to tackle typical object-oriented design difficulties. Because Java is object-oriented, skilled Java developers are familiar with object-oriented design principles and can construct their programs in an OO manner. They should be familiar with and have expertise with design patterns such as Singleton, Factory, Iterator, Builder, Object Pool, Fly-weight, Strategy, Visitor, and Composite.


Senior Java developers should be well-versed in concurrency and multi-threading.

Memory Management and JVM

Senior Java Developers must be well-versed in runtime and garbage collection. They must grasp when memory is allocated, what context it is allocated, and how this affects heap fragmentation. Memory leaks and mistakes are typical in data-intensive applications. They must be able to read code, comprehend memory flaws, repair them, and increase performance.

They must be knowledgeable about various trash collection strategies as well as how to use profilers. Senior developers should understand how to optimize it as well as when it is activated.


Database expertise is required for almost all Java developers. Even junior developers should have a solid understanding of SQL concepts such as queries, inner and outer joins, aggregations, joins, triggers, cursors, etc.

Frameworks and libraries

Java does not operate in isolation; rather, it is supported by a robust ecosystem of libraries and frameworks. Java developers must deal with various tools, including Struts, Spring, Hibernate, Gradle, Maven, Ant, JUnit, and Spock, depending on their position. When you ask a Java developer which frameworks they have previously worked with, you may get a good idea of how much time they have spent working on Java.


Developers may also need algorithmic skills depending on the position.

Communication abilities

Communication abilities are frequently the difference between a strong developer and an average developer. Developers must be able to express their ideas as well as collaborate with and coach other developers.

Furthermore, if the position required networking or distributed applications, they would need to be familiar with IP, HTTP, TCP, Sockets, FTP, UDP, RMI, and RCP.

A candidate for a post that entails working on Java UI should have experience with Applets and frameworks such as Swing, SWT, AWT, or JavaFX.

If the work involves developing Java-based web applications, the candidate must be skilled in the following areas:

  • Servlets / JSP
  • SOAP / REST – Service Oriented Architecture / Web Services
  • Web technologies, for example, HTML, CSS, Javascript, and JQuery
  • Web frameworks, for example, Struts / Spring
  • Markup languages such as XML and JSON.

The Java ecosystem is continually evolving. Therefore they must be willing to step outside of their comfort zone, learn new technologies, and accept challenges.

How to evaluate Java skills?

Screening developers is difficult since an estimated 85% of candidates lie on their résumé.

Recruiters frequently employ online screening tests, such as the Java Online Test, to conduct the initial round of screening and pre-selected the top 20% of qualified applicants to submit to hiring managers/clients.

Today, more and more firms are using coding tests to assess Java expertise. If you’ve never taken a coding test before, here’s how it works:

Setting up the test: You may build up a coding test using a skills assessment platform like KillerCoder or do it yourself. If you just have 3-5 applicants to evaluate and it is a one-time use case, setting it up yourself could be a good choice because you won’t have to spend time researching and selecting alternative solutions. This may become incredibly time-consuming when you have hundreds of applicants because you/your technical team will have to personally review each candidate’s solutions. Furthermore, you may not have the in-house knowledge to assess Java skills. This is where the use of a third-party skills evaluation tool comes in handy.

Inviting applicants to take the test: After you’ve put up your test, you may invite candidates who apply to take it. The ability to invite applicants from the dashboard is available on all assessment systems.

Evaluate and interview: Once applicants have completed the coding test, proceed quickly to interview software engineers who performed well on the assessment.