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for循环的字节码

发布时间:2023-12-01 15:04:44 222

源代码:

public class Wizard {
private int age;

private void forCycle() {
for (int i = 0; i < 10; i++) {
System.out.println(i);
}
}
}

javap -v -p Wizard.class 得到class文件:

Classfile /D:/Users/Administrator/workspace/TestJava/bin/com/bytecode/Wizard.class
Last modified 2018-3-17; size 545 bytes
MD5 checksum 529c4f32d75aa1bdce39f2b8fa128d76
Compiled from "Wizard.java"
public class com.bytecode.Wizard
SourceFile: "Wizard.java"
minor version: 0
major version: 51
flags: ACC_PUBLIC, ACC_SUPER

Constant pool:
#1 = Class #2 // com/bytecode/Wizard
#2 = Utf8 com/bytecode/Wizard
#3 = Class #4 // java/lang/Object
#4 = Utf8 java/lang/Object
#5 = Utf8 age
#6 = Utf8 I
#7 = Utf8
#8 = Utf8 ()V
#9 = Utf8 Code
#10 = Methodref #3.#11 // java/lang/Object."":()V
#11 = NameAndType #7:#8 // "":()V
#12 = Utf8 LineNumberTable
#13 = Utf8 LocalVariableTable
#14 = Utf8 this
#15 = Utf8 Lcom/bytecode/Wizard;
#16 = Utf8 forCycle
#17 = Fieldref #18.#20 // java/lang/System.out:Ljava/io/PrintStream;
#18 = Class #19 // java/lang/System
#19 = Utf8 java/lang/System
#20 = NameAndType #21:#22 // out:Ljava/io/PrintStream;
#21 = Utf8 out
#22 = Utf8 Ljava/io/PrintStream;
#23 = Methodref #24.#26 // java/io/PrintStream.println:(I)V
#24 = Class #25 // java/io/PrintStream
#25 = Utf8 java/io/PrintStream
#26 = NameAndType #27:#28 // println:(I)V
#27 = Utf8 println
#28 = Utf8 (I)V
#29 = Utf8 i
#30 = Utf8 StackMapTable
#31 = Utf8 SourceFile
#32 = Utf8 Wizard.java
{
private int age;
flags: ACC_PRIVATE


public com.bytecode.Wizard();
flags: ACC_PUBLIC

Code:
stack=1, locals=1, args_size=1
0: aload_0
1: invokespecial #10 // Method java/lang/Object."":()V
4: return
LineNumberTable:
line 3: 0
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this Lcom/bytecode/Wizard;

private void forCycle();
flags: ACC_PRIVATE

Code:
stack=2, locals=2, args_size=1
0: iconst_0
1: istore_1
2: goto 15
5: getstatic #17 // Field java/lang/System.out:Ljava/io/PrintStream;
8: iload_1
9: invokevirtual #23 // Method java/io/PrintStream.println:(I)V
12: iinc 1, 1
15: iload_1
16: bipush 10
18: if_icmplt 5
21: return
LineNumberTable:
line 7: 0
line 8: 5
line 7: 12
line 10: 21
LocalVariableTable:
Start Length Slot Name Signature
0 22 0 this Lcom/bytecode/Wizard;
2 19 1 i I
StackMapTable: number_of_entries = 2
frame_type = 252 /* append */
offset_delta = 5
locals = [ int ]
frame_type = 9 /* same */

}

分析for循环的字节码:

字节码

描述

操作数栈

iconst_0

0入栈

0

istore_1

把0赋值给局部变量i

 

goto 15

跳转到第15行

 

iload_1

局部变量i的值入栈

0

bipush 10

10入栈

0, 10

if_icmplt 5

比较0和10,小于则跳到第5行

 

getstatic #17

System.out入栈

Systme.out

iload_1

局部变量i的值入栈

System.out, 0

invokevirtual #23

调用print方法

 

iinc 1, 1

局部变量i自增1

 

iload_1

把i的值入栈

2

 

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