In which programming language is Hadoop primarily written?

Hadoop is primarily written in Java, which is significant for its platform independence and the ability to run on any machine that has a Java Virtual Machine (JVM). This design choice allows Hadoop to be deployed in a variety of environments and ensures compatibility across different operating systems. Java's multithreading capabilities and robust performance are also critical for processing large datasets efficiently, which is a key feature of Hadoop. The use of Java provides developers with a familiar object-oriented programming environment, enabling them to create reliable and scalable applications that can process vast amounts of data across distributed systems.

The other languages listed—Python, C++, and Ruby—are often used in conjunction with Hadoop for various tasks, such as data processing or scripting, but they are not the foundational languages of the Hadoop framework itself.