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在谈论JVM-运行时数据区时，我们遇到了一个方法区，关于方法区的信息都来自于class，在JDK的工具中，有一个javap命令可以用来显示class文件的信息。
查看class文件内容的命令如下：
javap -v XXX.clsss 1 1
在这里以TestClass.示例
/** * */package com.hx;import com.hx.vo.BaseParam;/** * @author MichaelKoo * * 2017-7-12 */public class TestClass extends BaseParam implements Runnable { private String name; private static final int AGE = 18; public void run() { name = "MichaelKoo," + AGE; try { CsdnUtil.getContent(getClass()); } catch (Exception e) { e.printStackTrace(); } }} 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 编译成TestClass.class之后，使用javap命令打开信息如下：
Classfile /I:/adt_eclipse_work/HuanXinTest/bin/com/hx/TestClass.class Last modified 2017-7-12; size 785 bytes MD5 checksum 92698cfe5ce5c5322fa75fe4c2a54b2e Compiled from "TestClass.java"public class com.hx.TestClass extends com.hx.vo.BaseParam implements java.lang.Runnable minor version: 0 major version: 51 flags: ACC_PUBLIC, ACC_SUPERConstant pool: #1 = Class #2 // com/hx/TestClass #2 = Utf8 com/hx/TestClass #3 = Class #4 // com/hx/vo/BaseParam #4 = Utf8 com/hx/vo/BaseParam #5 = Class #6 // java/lang/Runnable #6 = Utf8 java/lang/Runnable #7 = Utf8 name #8 = Utf8 Ljava/lang/String; #9 = Utf8 AGE #10 = Utf8 I #11 = Utf8 ConstantValue #12 = Integer 18 #13 = Utf8 #14 = Utf8 ()V #15 = Utf8 Code #16 = Methodref #3.#17 // com/hx/vo/BaseParam." ":()V #17 = NameAndType #13:#14 // " ":()V #18 = Utf8 LineNumberTable #19 = Utf8 LocalVariableTable #20 = Utf8 this #21 = Utf8 Lcom/hx/TestClass; #22 = Utf8 run #23 = String #24 // MichaelKoo,18 #24 = Utf8 MichaelKoo,18 #25 = Fieldref #1.#26 // com/hx/TestClass.name:Ljava/lang/String; #26 = NameAndType #7:#8 // name:Ljava/lang/String; #27 = Methodref #28.#30 // java/lang/Object.getClass:()Ljava/lang/Class; #28 = Class #29 // java/lang/Object #29 = Utf8 java/lang/Object #30 = NameAndType #31:#32 // getClass:()Ljava/lang/Class; #31 = Utf8 getClass #32 = Utf8 ()Ljava/lang/Class; #33 = Methodref #34.#36 // com/hx/CsdnUtil.getContent:(Ljava/lang/Class;)Ljava/lang/String; #34 = Class #35 // com/hx/CsdnUtil #35 = Utf8 com/hx/CsdnUtil #36 = NameAndType #37:#38 // getContent:(Ljava/lang/Class;)Ljava/lang/String; #37 = Utf8 getContent #38 = Utf8 (Ljava/lang/Class;)Ljava/lang/String; #39 = Methodref #40.#42 // java/lang/Exception.printStackTrace:()V #40 = Class #41 // java/lang/Exception #41 = Utf8 java/lang/Exception #42 = NameAndType #43:#14 // printStackTrace:()V #43 = Utf8 printStackTrace #44 = Utf8 e #45 = Utf8 Ljava/lang/Exception; #46 = Utf8 StackMapTable #47 = Utf8 SourceFile #48 = Utf8 TestClass.java{ public com.hx.TestClass(); descriptor: ()V flags: ACC_PUBLIC Code: stack=1, locals=1, args_size=1 0: aload_0 1: invokespecial #16 // Method com/hx/vo/BaseParam." ":()V 4: return LineNumberTable: line 13: 0 LocalVariableTable: Start Length Slot Name Signature 0 5 0 this Lcom/hx/TestClass; public void run(); descriptor: ()V flags: ACC_PUBLIC Code: stack=2, locals=2, args_size=1 0: aload_0 1: ldc #23 // String MichaelKoo,18 3: putfield #25 // Field name:Ljava/lang/String; 6: aload_0 7: invokevirtual #27 // Method java/lang/Object.getClass:()Ljava/lang/Class; 10: invokestatic #33 // Method com/hx/CsdnUtil.getContent:(Ljava/lang/Class;)Ljava/lang/String; 13: pop 14: goto 22 17: astore_1 18: aload_1 19: invokevirtual #39 // Method java/lang/Exception.printStackTrace:()V 22: return Exception table: from to target type 6 14 17 Class java/lang/Exception LineNumberTable: line 18: 0 line 21: 6 line 22: 14 line 23: 18 line 25: 22 LocalVariableTable: Start Length Slot Name Signature 0 23 0 this Lcom/hx/TestClass; 18 4 1 e Ljava/lang/Exception; StackMapTable: number_of_entries = 2 frame_type = 81 /* same_locals_1_stack_item */ stack = [ class java/lang/Exception ] frame_type = 4 /* same */}SourceFile: "TestClass.java" 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110
其中有几个需要关注的节点：
- 类的信息，在关键字’Constant pool:’之前就属于类的基本信息，从中可以看出，类的修饰符(public )、类的完整名称(com.hx.TestClass)、类的父类完整名称(com.hx.vo.BaseParam)、类的接口信息(java.lang.Runnable)
- 常量池，在关键字’Constant pool:’之后，第一个’{‘之前的内容就属于常量池信息，
- 在’{‘之后，’}’之前就是类的方法信息，从中可以看出:方法的修饰符、方法的返回值类型、方法名称、方法的异常表、方法的局部变量表等信息
转载地址：http://blog.csdn.net/android_app/article/details/75043072