Final answer:
Java bytecode files have the .class extension, which is generated after the Java source code is compiled. This intermediate representation allows Java to be platform-independent.
Step-by-step explanation:
The extension used by Java bytecode files is .class. After a Java source code file (with a .java extension) is compiled by the Java compiler, it is transformed into bytecode with the .class extension. This bytecode is the intermediate representation of your program that the Java Virtual Machine (JVM) understands and can execute on any platform that has JVM installed, which is why Java is known as a platform-independent language.