Java class 文件时对Java程序二进制文件格式的精确定义。
一个class文件只能包含一个类或接口。
Java class文件是8位字节的二进制流。
在Java class文件中，可变长度项的大小和长度位于其实际数据之前。
class文件的基本类型
u1 1byte 无符号类型
u2 2byte 无符号类型
u4 4byte 无符号类型
u8 8byte 无符号类型
==========================================
以下是Java源码文件
public class ClassTest {
final static int constantInt=12;
final static String constantString="我很好";
static int variableInt=12;
static String variableString="我很好";
private int variable;
private String variable2;
public static void main(String[] args) {
System.out.println("--这是main()方法---");
}
public void say() {
System.out.println("这是普通方法");
}
public ClassTest(int variable, String variable2) {
super();
this.variable = variable;
this.variable2 = variable2;
}
public ClassTest() {
}
以下是使用uedit 编辑器查看的字节码文件
以下是使用 javap -v ClssTest.class 查看的字节码文件内容
Last modified 2019-7-24; size 924 bytes
MD5 checksum be5b20653620d7d2b495a3f99e3fb417
Compiled from "ClassTest.java"
public class ClassTest
minor version: 0
major version: 52
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Fieldref #34.#35 // java/lang/System.out:Ljava/io/PrintStream;
#2 = String #36 // --这是main()方法---
#3 = Methodref #37.#38 // java/io/PrintStream.println:(Ljava/lang/String;)V
#4 = String #39 // 这是普通方法
#5 = Methodref #12.#40 // java/lang/Object."<init>":()V
#6 = Fieldref #11.#41 // ClassTest.variable:I
#7 = Fieldref #11.#42 // ClassTest.variable2:Ljava/lang/String;
#8 = Fieldref #11.#43 // ClassTest.variableInt:I
#9 = String #44 // 我很好
#10 = Fieldref #11.#45 // ClassTest.variableString:Ljava/lang/String;
#11 = Class #46 // ClassTest
#12 = Class #47 // java/lang/Object
#13 = Utf8 constantInt
#14 = Utf8 I
#15 = Utf8 ConstantValue
#16 = Integer 12
#17 = Utf8 constantString
#18 = Utf8 Ljava/lang/String;
#19 = Utf8 variableInt
#20 = Utf8 variableString
#21 = Utf8 variable
#22 = Utf8 variable2
#23 = Utf8 main
#24 = Utf8 ([Ljava/lang/String;)V
#25 = Utf8 Code
#26 = Utf8 LineNumberTable
#27 = Utf8 say
#28 = Utf8 ()V
#29 = Utf8 <init>
#30 = Utf8 (ILjava/lang/String;)V
#31 = Utf8 <clinit>
#32 = Utf8 SourceFile
#33 = Utf8 ClassTest.java
#34 = Class #48 // java/lang/System
#35 = NameAndType #49:#50 // out:Ljava/io/PrintStream;
#36 = Utf8 --这是main()方法---
#37 = Class #51 // java/io/PrintStream
#38 = NameAndType #52:#53 // println:(Ljava/lang/String;)V
#39 = Utf8 这是普通方法
#40 = NameAndType #29:#28 // "<init>":()V
#41 = NameAndType #21:#14 // variable:I
#42 = NameAndType #22:#18 // variable2:Ljava/lang/String;
#43 = NameAndType #19:#14 // variableInt:I
#44 = Utf8 我很好
#45 = NameAndType #20:#18 // variableString:Ljava/lang/String;
#46 = Utf8 ClassTest
#47 = Utf8 java/lang/Object
#48 = Utf8 java/lang/System
#49 = Utf8 out
#50 = Utf8 Ljava/io/PrintStream;
#51 = Utf8 java/io/PrintStream
#52 = Utf8 println
#53 = Utf8 (Ljava/lang/String;)V
{
static final int constantInt;
descriptor: I
flags: ACC_STATIC, ACC_FINAL
ConstantValue: int 12
static final java.lang.String constantString;
descriptor: Ljava/lang/String;
flags: ACC_STATIC, ACC_FINAL
ConstantValue: String 我很好
static int variableInt;
descriptor: I
flags: ACC_STATIC
static java.lang.String variableString;
descriptor: Ljava/lang/String;
flags: ACC_STATIC