- They are both programming languages.
- The word "Java".
- Both came out of the web technology explosion of the early 1990s.
- Both are frequently encountered in the context of web browsers.
Java is associated with the web browser experience because of the widespread use of Java "applets" that are embedded in browser windows. Applets are not technically part of the browser; the compiled Java bytecode is downloaded by the browser and executed in a Java Virtual Machine (JVM) as a separate process. Applets are frequently transferred as a compressed "Java archive", or JAR file. Applets downloaded by a browser do not necessarily need to run in a browser window, but the fact that they are frequently embedded there leads to some confusion.
Neither is Java necessarily a client-side technology: many popular server-side applications are written in Java and execute in a server-side JVM. Google's Android platform extends things even further, using Java as the programming language but compiling the bytecode to execute on their own proprietary virtual machine.