The MIME type application/java is used to denote the presence of Java bytecode instruction format files. The category of this MIME type is "application".

The Java bytecode files use the extension CLASS. These are generated by the Java compiler while handling a Java application and are executed by the Java virtual machine. Although each bytecode opcode is one byte in length (8 bits), the requirement of parameters by some creates multi-byte instructions for the Java virtual machines. There are exactly 256 possible opcodes defined for this purpose. However, not all of them are used. The creators of the Java programming language, the Java virtual machine and the rest of the Java Runtime Environment (JRE) � Sun Microsystems have actually set aside 3 of these values for keeping them permanently unimplemented.

Technically, a Java programmer requires absolutely no knowledge of the Java bytecode instructions. However, learning about Java bytecode can help a programmer to develop more robust applications since he will know how to anticipate the Java bytecodes that may be generated by the machine. It has been compared to the advantages of knowing Assembly while programming in C or C++ by the IBM developerWorks journal.