Java bytecode

Java bytecode is the form of instructions that the Java virtual machine executes. Each bytecode instruction is one byte in length (hence the name), thus the number of bytecodes is limited to no more than 256. Not all 256 possible bytecode values are used, in fact Sun Microsystems, the original creators of the Java programming language, the Java virtual machine and other components of the Java Runtime Environment, have permanently set aside a number of values to be permanently unimplemented. The bytecodes are given below.

The Java bytecodes

Please see Sun's Java Virtual Machine Specification for more detailed descriptions (link at bottom of page)

Mnemonic	Opcode (in hex)	Description
aaload	32	loads onto the stack a reference to an array
aastore	53	stores into a reference to an array
aconst_null	01	pushes a null reference onto the stack
aload	19	loads a reference onto the stack from a local variable
aload_0	2a	loads a reference from local variable 0
aload_1	2b	loads a reference from local variable 1
aload_2	2c	loads a reference from local variable 2
aload_3	2d	loads a reference from local variable 3
anewarray	bd	creates a new array of references
areturn	b0	returns a reference from a method
arraylength	be	gets the length of an array
astore	3a	stores a reference into a local variable
astore_0	4b	stores a reference into local variable 0
astore_1	4c	stores a reference into local variable 1
astore_2	4d	stores a reference into local variable 2
astore_3	4e	stores a reference into local variable 3
athrow	bf	throws an error or exception
baload	33	loads a byte or boolean value from an array
bastore	54	stores a byte or boolean value into an array
bipush	10	pushes a byte onto the stack
caload	34	loads a char from an array
castore	55	stores a char into an array
checkcast	c0	checks whether an object is of a certain type
d2f	90	converts a double to a float
d2i	8e	converts a double to an int
d2l	8f
dadd	63
daload	31
dastore	52
dcmpg	98
dcmpl	97
dconst_0	0e
dconst_1	0f
ddiv	6f
dload	18
dload_0	26	loads a double from local variable 0
dload_1	27	loads a double from local variable 1
dload_2	28	loads a double from local variable 2
dload_3	29	loads a double from local variable 3
dmul	6b
dneg	77
drem	73
dreturn	af
dstore	39
dstore_0	47	stores a double into local variable 0
dstore_1	48	stores a double into local variable 1
dstore_2	49	stores a double into local variable 2
dstore_3	4a	stores a double into local variable 3
dsub	67
dup	59
dup_x1	5a
dup_x2	5b
dup2	5c
dup2_x1	5d
dup2_x2	5e

more to be added later

External links

• Sun's Java Virtual Machine Specification