"Java is one of the most popular programming languages in the world, and for good reason. It is versatile, easy to learn, and has a large ecosystem of libraries and frameworks that can be used to develop a wide range of applications.

Many large companies have recognized the benefits of using Java and have chosen to use it as the primary language for their core product development. Some examples of companies that use Java include Amazon, eBay, LinkedIn, Uber, Airbnb, Netflix, Twitter, Spotify, and Google.

Amazon, for example, uses Java to develop many of its e-commerce websites and services. The company has also developed a number of open-source libraries and frameworks that are used by other developers to build Java-based applications.

eBay also uses Java for its core product development. The company has built a number of large-scale, high-performance systems using Java, such as its search engine and its recommendation system.

LinkedIn, another company that uses Java, has built a number of its core features such as its job search and professional networking features using Java.

Uber, Airbnb, Netflix, Twitter, and Spotify are also examples of companies that have chosen Java as the primary language for their core product development. Uber uses Java for its ride-hailing app, Airbnb for its vacation rental platform, Netflix for its streaming service, Twitter for its microblogging platform, and Spotify for its music streaming service.

Google, another major player in the tech industry, uses Java for many of its products and services, including the development of its Android operating system.

These are just a few examples of the many companies that use Java for their core product development. The list goes on and on, and it's clear that Java is a language that is here to stay.

In conclusion, Java is a powerful and versatile programming language that has proven to be an excellent choice for many companies looking to develop their core products. From e-commerce websites to ride-hailing apps and streaming services, Java has been used to build some of the most popular and successful products on the market today. If you're looking to build a career in software development, learning Java is a great place to start."