前言
从字节码看java中 this 隐式传参具体体现（和python中的self如出一辙，但是比python中藏得更深），也发现了 static 与 非 static 方法的区别所在！
static与非static方法都是存储java的方法区。在static 方法中，没有this引用，因此无法使用当前类中所定义的变量，而非static方法则会默认传入this。
概述
this关键字，是一个隐式参数，另外一个隐式参数是super。 this用于方法里面，用于方法外面无意义。 this关键字一般用于set方法和构造方法中。我们今天就从另一个角度来真实看一下这个答案吧！
来个例子，并将其反编译为可视代码:
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public class hello {
private final int ii;
public hello( int a) { ii = a; }
public static void main(string[] args) throws exception { sayhellostatic( "ok" ); }
public void sayhello(string word) { system.out.println( "hello, " + word); } public static void sayhellostatic(string word) { system.out.println( "static hello, " + word); } } |
反汇编命令：
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javap -verbose hello. class |
反汇编结果：
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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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 |
classfile /d:/xx/target/classes/com/xx/api/hello. class last modified 2018 - 11 - 8 ; size 1069 bytes md5 checksum 9d39cd9d4e95588a73c059a4e69f01e8 compiled from "hello.java" public class com.xx.api.hello minor version: 0 major version: 52 flags: acc_public, acc_super constant pool: # 1 = methodref # 14 .# 38 // java/lang/object."<init>":()v # 2 = fieldref # 13 .# 39 // com/xx/api/hello.ii:i # 3 = string # 40 // ok # 4 = methodref # 13 .# 41 // com/xx/api/hello.sayhellostatic:(ljava/lang/string;)v # 5 = fieldref # 42 .# 43 // java/lang/system.out:ljava/io/printstream; # 6 = class # 44 // java/lang/stringbuilder # 7 = methodref # 6 .# 38 // java/lang/stringbuilder."<init>":()v # 8 = string # 45 // hello, # 9 = methodref # 6 .# 46 // java/lang/stringbuilder.append:(ljava/lang/string;)ljava/lang/stringbuilder; # 10 = methodref # 6 .# 47 // java/lang/stringbuilder.tostring:()ljava/lang/string; # 11 = methodref # 48 .# 49 // java/io/printstream.println:(ljava/lang/string;)v # 12 = string # 50 // static hello, # 13 = class # 51 // com/xx/api/hello # 14 = class # 52 // java/lang/object # 15 = utf8 ii # 16 = utf8 i # 17 = utf8 <init> # 18 = utf8 (i)v # 19 = utf8 code # 20 = utf8 linenumbertable # 21 = utf8 localvariabletable # 22 = utf8 this # 23 = utf8 lcom/xx/api/hello; # 24 = utf8 a # 25 = utf8 main # 26 = utf8 ([ljava/lang/string;)v # 27 = utf8 args # 28 = utf8 [ljava/lang/string; # 29 = utf8 exceptions # 30 = class # 53 // java/lang/exception # 31 = utf8 sayhello # 32 = utf8 (ljava/lang/string;)v # 33 = utf8 word # 34 = utf8 ljava/lang/string; # 35 = utf8 sayhellostatic # 36 = utf8 sourcefile # 37 = utf8 hello.java # 38 = nameandtype # 17 :# 54 // "<init>":()v # 39 = nameandtype # 15 :# 16 // ii:i # 40 = utf8 ok # 41 = nameandtype # 35 :# 32 // sayhellostatic:(ljava/lang/string;)v # 42 = class # 55 // java/lang/system # 43 = nameandtype # 56 :# 57 // out:ljava/io/printstream; # 44 = utf8 java/lang/stringbuilder # 45 = utf8 hello, # 46 = nameandtype # 58 :# 59 // append:(ljava/lang/string;)ljava/lang/stringbuilder; # 47 = nameandtype # 60 :# 61 // tostring:()ljava/lang/string; # 48 = class # 62 // java/io/printstream # 49 = nameandtype # 63 :# 32 // println:(ljava/lang/string;)v # 50 = utf8 static hello, # 51 = utf8 com/xx/api/hello # 52 = utf8 java/lang/object # 53 = utf8 java/lang/exception # 54 = utf8 ()v # 55 = utf8 java/lang/system # 56 = utf8 out # 57 = utf8 ljava/io/printstream; # 58 = utf8 append # 59 = utf8 (ljava/lang/string;)ljava/lang/stringbuilder; # 60 = utf8 tostring # 61 = utf8 ()ljava/lang/string; # 62 = utf8 java/io/printstream # 63 = utf8 println { public com.xx.api.hello( int ); descriptor: (i)v flags: acc_public code: stack= 2 , locals= 2 , args_size= 2 0 : aload_0 1 : invokespecial # 1 // method java/lang/object."<init>":()v 4 : aload_0 5 : iload_1 6 : putfield # 2 // field ii:i 9 : return linenumbertable: line 14 : 0 line 15 : 4 line 16 : 9 localvariabletable: start length slot name signature 10 0 this lcom/xx/api/hello; 10 1 a i
public static void main(java.lang.string[]) throws java.lang.exception; descriptor: ([ljava/lang/string;)v flags: acc_public, acc_static code: stack= 1 , locals= 1 , args_size= 1 0 : ldc # 3 // string ok 2 : invokestatic # 4 // method sayhellostatic:(ljava/lang/string;)v 5 : return linenumbertable: line 42 : 0 line 45 : 5 localvariabletable: start length slot name signature 6 0 args [ljava/lang/string; exceptions: throws java.lang.exception
public void sayhello(java.lang.string); descriptor: (ljava/lang/string;)v flags: acc_public code: stack= 3 , locals= 2 , args_size= 2 0 : getstatic # 5 // field java/lang/system.out:ljava/io/printstream; 3 : new # 6 // class java/lang/stringbuilder 6 : dup 7 : invokespecial # 7 // method java/lang/stringbuilder."<init>":()v 10 : ldc # 8 // string hello, 12 : invokevirtual # 9 // method java/lang/stringbuilder.append:(ljava/lang/string;)ljava/lang/stringbuilder; 15 : aload_1 16 : invokevirtual # 9 // method java/lang/stringbuilder.append:(ljava/lang/string;)ljava/lang/stringbuilder; 19 : invokevirtual # 10 // method java/lang/stringbuilder.tostring:()ljava/lang/string; 22 : invokevirtual # 11 // method java/io/printstream.println:(ljava/lang/string;)v 25 : return linenumbertable: line 48 : 0 line 49 : 25 localvariabletable: start length slot name signature 26 0 this lcom/xx/api/hello; 26 1 word ljava/lang/string;
public static void sayhellostatic(java.lang.string); descriptor: (ljava/lang/string;)v flags: acc_public, acc_static code: stack= 3 , locals= 1 , args_size= 1 0 : getstatic # 5 // field java/lang/system.out:ljava/io/printstream; 3 : new # 6 // class java/lang/stringbuilder 6 : dup 7 : invokespecial # 7 // method java/lang/stringbuilder."<init>":()v 10 : ldc # 12 // string static hello, 12 : invokevirtual # 9 // method java/lang/stringbuilder.append:(ljava/lang/string;)ljava/lang/stringbuilder; 15 : aload_0 16 : invokevirtual # 9 // method java/lang/stringbuilder.append:(ljava/lang/string;)ljava/lang/stringbuilder; 19 : invokevirtual # 10 // method java/lang/stringbuilder.tostring:()ljava/lang/string; 22 : invokevirtual # 11 // method java/io/printstream.println:(ljava/lang/string;)v 25 : return linenumbertable: line 51 : 0 line 52 : 25 localvariabletable: start length slot name signature 26 0 word ljava/lang/string; } sourcefile: "hello.java" |
我们从字节码文件中可以看出来：
sayhello(string word) 和 sayhellostatic(string word) 都只有一个参数，但是在字节码中：
sayhello(string word) 中引用 word 时使用了 15: aload_1, 可以看出其加载的变量是在 slot1中，而 slot0中即保存了 this 。
sayhellostatic(string word) 中引用 word 时使用了 15: aload_0, 可以看出静态方法中，直接将变量存在了 slot0中，因此无法使用 this 中的变量了。
当要操作当前类的变量或方法时，需要先 aload_0, 然后再做相关操作！
总结：
以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作具有一定的参考学习价值，如果有疑问大家可以留言交流，谢谢大家对的支持。
原文链接：http://HdhCmsTestcnblogs测试数据/yougewe/p/9929249.html
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