Most of the opcodes have zero or one operands, usually a single byte (or two bytes with a prefix) that's an index into the local variable array or the constant pool. There's several ways to load constants: the integer constants -1 through 5, long constants 0 and 1, float and double 0, 1, and 2 all have 0-operand opcodes (e.g., iconst_0); there's an opcode to load a 1-byte immediate, another to load a two-byte immediate, and an opcode to load a constant in the constant pool (which can be a string, a Class<?> reference, an integer, long, double, or float).

It should be noted that the JVM specifies a fixed big-endian format in its bytecode, and as a result, even the two-byte immediates are specified in the manual as two operands of a single byte each.

Constants that fit in a byte don't have this problem and can be easily placed in the instruction stream using dedicated byte constant instructions, sometimes including dedicated single-byte instructions for common constants like zero, one, etc.