Java bytecode is the form of instructions that the Java virtual machine executes. Each bytecode opcode is one byte in length, although some require parameters, resulting in some multi-byte instructions. Not all of the possible 256 opcodes are used. 51 are reserved for future use. Beyond that, Sun Microsystems, the original creators of the Java programming language, the Java virtual machine and other components of the Java Runtime Environment (JRE), have set aside three values to be permanently unimplemented.
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