What is Java bytecode?

Java bytecode is the form of instructions that the Java virtual machine executes. Every bytecode instruction is one byte in length (hence the name), therefore the number of bytecodes is limited to 256. Not all 256 probable bytecode values are used. Actually, Sun Microsystems, the inventive creators of the Java programming language, the Java virtual machine and the added components of the Java Runtime Environment, have set aside a number of values to be lastingly unimplemented.