iinc

Increment local variable by constant

Bytecode

For local variable numbers in the range 0-255, and values of <n> in the range -128 to 127, use:

Type Description
u1 iinc opcode = 0x84 (132)
u1 <varnum>
s1 <n>

There is also a wide format for this instruction, which supports access to all local variables from 0 to 65535, and values of <n> between -32768 and 32767:

Type Description
u1 wide opcode = 0xC4 (196)
u1 iinc opcode = 0x84 (132)
u2 <varnum>
s2 <n>

Stack No change

Description

iinc increments the int held in the local variable <varnum> by <n>. The iinc instruction takes two parameters:

<varnum> is an unsigned integer which indicates which local variable should be used.

<n> is the integer amount to increment or decrement the variable by. <varnum> must be a valid local variable number in the current method's frame.

Example

iinc 1 10       ; increment local variable 1 by 10.
iinc 1 -1       ; decrement local variable 1 by 1.

Notes

The iinc opcode can be used in conjunction with the wide instruction to access a local variable using a two-byte unsigned index and increment it by a two-byte immediate value.