The two languages offer a decent balance between high pay while still being in-demand, according to job postings in the 12 months to the start of this year.
The languages naturally complement each other, with Kotlin able to be used as a replacement for Java in many instances as it runs on the same underlying platform, the Java Virtual Machine (JVM).
The open-source, statically-typed language gained major traction in 2017 when Google threw its weight behind Kotlin and designated it an officially supported language for building Android apps.
Kotlin has been described by a Netflix senior software engineer as offering
"some of the best features of other languages" combined with "interoperability with Java". There is even speculation that it will eventually replace Java for Android development.
Meanwhile, Java remains widely in use and reasonably well-paid, thanks to language's status as the workhorse of the modern enterprise, having been the language of choice for writing server-side business software for more than a decade. Beyond business, Java is also an official language used for developing Android apps and is also used for games and web apps.
Both languages were among the few that were both in demand and well paid throughout 2018 according to IT Jobs Watch, which gathers and analyzes data from UK IT job vacancies.
According to IT Jobs Watch, the top five languages in terms of earnings in the 12 months to December 2018 were:
While the languages most often requested by employers during the same period were:
Recruitment site Indeed also found strong demand for Java skills in the US in its analysis of tech-related job postings in the middle of last year, while both Kotlin and Java were also listed among the languages associated with the highest paying developer roles in the US in the 2018 Stack Overflow Developer Survey
That demand for Java is reflected in figures from UK recruitment company Hays, with Java developer being one of the top five highest paying roles throughout 2018.
That said, the higher salaries are reserved for experienced web developers, for example, front-end developers skilled in using UI design frameworks such as Angular and React, and starting salaries for web developers are significantly lower.
Hay's Milligan says demand for web frontend and backend skills, alongside Java, had remained strong year-in, year-out.
The other languages that offer the highest salaries are Scala, Go and Groovy, as well as the data science and statistical analysis language R. While R is still the most commonly used language by data scientists at work, according to a recent Kaggle survey, there aren't a huge number of postings searching for Scala, Go and Groovy talent, so while they're well-compensated, it may be hard to find related work. Although given Scala is designed to be interoperable with Java, it may also be a good choice to learn alongside that language.
Skills in Go have commanded a premium for several years now in both the UK and the US and were identified as being among the top five highest paying languages in the US by the 2018 Stack Overflow Developer Survey