6.2. Reserved Opcodes

In addition to the opcodes of the instructions specified later in this chapter, which are used in class files (§4), three opcodes are reserved for internal use by a Java Virtual Machine implementation. If the instruction set of the Java Virtual Machine is extended in the future, these reserved opcodes are guaranteed not to be used.

Two of the reserved opcodes, numbers 254 (0xfe) and 255 (0xff), have the mnemonics impdep1 and impdep2, respectively. These instructions are intended to provide “back doors” or traps to implementation-specific functionality implemented in software and hardware, respectively. The third reserved opcode, number 202 (0xca), has the mnemonic breakpoint and is intended to be used by debuggers to implement ...

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