Operand stack
During operand stack for execution of bytecode instructions, just as a general purpose register in the CPU. Most JVM bytecode popping the respective operation, stack, copy, exchange, or perform the operation, so that various data of production and consumption. Thus, in the byte code, the command to move frequently between the value of the local variable table and the operand stack. For example, a simple interaction results in variable initialization operand stack where two bytecodes impact.
int i;
The following bytecode compiled from:
0: iconst_0 // 0 will push to the top of the operand stack.
1: istore_1 // pop top stack operands from and stored to a local variable
Integer JVM byte code of the push instruction (iconst, bipush, sipush, ldc)
java in shaping the common length indicates the range:
byte ranges from -128 to 127, 1 byte (-2 to 7 th to 7 th -12)
Short ranges from -32768 to 32767, 2 bytes (- 15 th to 15 th -1) 2 2
int ranges (-2147483648 to 2147483647), power 31 4 bytes (31 - 2 to the power of 2 -1)
Long a in the range (~ -9,223,372,036,854,774,808 9223372036854774807), 8 bytes (63 -2 to 63 th -12 th) of
When the value of int -1 to 5: int ranging from 0 to 5 JVM uses iconst_0, iconst_1, iconst_2, iconst_3, iconst_4, iconst_5 the constant instruction onto the stack, using iconst_m1 the constant instruction value onto the stack -1 the
value of -128 to 127 using bipush instruction (bipush 127),
the value -32768 to 32767 using sipush instruction (sipush 32767)
The value -2147483648 2147483647 ~ employed ldc instruction (ldc # 2; // int 2147483647 value obtained from the constant pool).
java stack
Thread - the thread's stack, the stack frame - method, thread execution method is to stack frame from the stack, the stack of the process.
Stack frame: three parts: local variables (variables + parameters in the method), and other data operand stack
| Bytecode |
Stack before->after |
Description |
| iconst_0 |
->0 |
Loads the int value 0 onto the stack |
| istore_1 |
value-> |
Store int value into variable 1 |
| istore_2 |
value-> |
Store int value into variable 2 |
| iinc |
No change |
Increment local variable #index by signed byte const |
| iload_1 |
->value |
Loads an int value from variable 1 |
| iadd |
value 1,value 2->result |
Adds 2 ints together |