java代码实现tcc代码 javac怎么弄

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mob6454cc7acbf7 2024-08-13 10:22:21

文章标签 java代码实现tcc代码 java c new java 字节码 System 文章分类 Java 后端开发

javac 概述

javac 是jdk bin目录下的一个脚本。用于编译 java程序的源代码，但是其实现的本质是基于 jdk 标准类库中的 javac类库实现，所以java的编译器实质上是一个 java程序。

javac脚本仅是一个便于启动以及传递参数的脚本文件，其内部依旧运行了 java程序。

javac 又被称作前端编译器，仅负责源代码与字节码之间的转换，而在jvm内部还存在一个后置编译器，根据热点探测技术可以将最有价值的字节码转换为机器码执行从而提升java程序的运行效率。

javac 的意义就在于将源码编译为字节码，同时做一些词法，语法，语义上的检查，最后生成可供jvm运行的字节码文件。

javac 源码

在 lib 中的 tools jar 包中 sun.tools.javac; 包下管理者 java前端编译器的class文件。 Main 类中的 main 方法的执行是javac程序的执行入口。

1 public static voidmain(String args[])2 {
//将标准错误流获取3 PrintStream printstream =System.err;4 if (Boolean.getBoolean("javac.pipe.output"))5 printstream =System.out;
//创建 编译器对象6 Main main1 = new Main(printstream, "javac");
//调用编译器的 compile方法进行 编译 并接受 args 为参数，该参数就是 javac 后面携带的参数7 System.exit(main1.compile(args) ? 0: main1.exitStatus);8 }

compile方法的编译过程概括性的分析:

1.解析与填充符号表

解析: 对java源代码的字节流进行读取解析，进行两个大致的步骤，词法解析以及语法解析

词法解析: 识别 java源码中存在的表达语义的逻辑单元，列如关键字变量名参数名每一个逻辑单元称为标量。

语法解析：将各个独立的标量按照java语法规范形成 java语法数，语法树的每一个节点代表一个操作，运算，或者方法调用。

填充符号表: 解析后的语法树最顶级的节点将被用来填充在符号表中，符号表存储着各个语法树的最顶级节点，填充后的符号表最终形成待处理表。

符号表就是一个遵从java语法的结构规范，用于组织语法树的逻辑顺序。

2.插入式注解处理器

jdk1.5后引入注解功能，注解是一种应用字节码属性中类的元数据进行操作的一种编程机制。

处理表形成后会自动检测是否有注解器需要执行，若有则执行注解处理器。注解处理器实现了在可插入式的编译期改变编译过程的功能。

其本质就是再次修改处理表中的语法树。一旦语法树被修改，则将再次进行词法，语法分析并填充符号表的过程。

3.语义分析并生成字节码

语义分析: 再次对语法树中的节点进行校验。对数据类型以及控制逻辑进行检测。

标量检测: 检验关键字是否使用正确，类型转换是否正确等。

数据与控制流分析: 对控制流程的逻辑进行校验。

语法糖解析: 编程语言为了增加代码的可读性，以及减少编程出错率，提供了一些并不影响程序运行期仅在编译期有效的编程机制。

java语言中语法糖有泛型，拆箱与装箱，foreach循环，可变参数，switch，枚举等，在编译期将转换为字节码遵守的规范形式。

泛型使用类型擦出，拆装箱调用了valueOf与xxValue方法，foreach是迭代器可变参数是数组，switch本质是 if else 的嵌套。

字节码替换: 在生成类的字节码之时，编译器后做一些默认性质的操作，当没有显示声明的构造器，则会创建默认的无参构造器，构造器分为实例构造器与类构造器

在字节码层面类构造器是指多个static代码块中的语句收敛生成的指令。而构造代码块与显示的构造器将收敛生成实例构造器。

同时还会将 String类型的 +与+= 操作，默认替换为对 StringBuffer或 StrignBudiuer的操作。

最后生成字节码。

代码如下:

1 public synchronized booleancompile(String as[])2 {3 String s = null;4 String s1 = null;5 String s2 = null;6 String s3 = null;7 boolean flag = false;8 String s4 = null;9 short word0 = 45;10 short word1 = 3;11 File file = null;12 File file1 = null;13 String s5 = "-Xjcov";14 String s6 = "-Xjcov:file=";15 int i = 0x41004;16 long l =System.currentTimeMillis();17 Vector vector = newVector();18 boolean flag1 = false;19 Object obj = null;20 String s7 = null;21 String s8 = null;22 String s9 = null;23 exitStatus = 0;24 try
25 {26 as =CommandLine.parse(as);27 }28 catch(FileNotFoundException filenotfoundexception)29 {30 error("javac.err.cant.read", filenotfoundexception.getMessage());31 System.exit(1);32 }33 catch(IOException ioexception)34 {35 ioexception.printStackTrace();36 System.exit(1);37 }38 label0:39 for (int j = 0; j < as.length; j++)40 {41 if (as[j].equals("-g"))42 {43 if (s8 != null && !s8.equals("-g"))44 error("main.conflicting.options", s8, "-g");45 s8 = "-g";46 i |= 0x1000;47 i |= 0x2000;48 i |= 0x40000;49 continue;50 }51 if (as[j].equals("-g:none"))52 {53 if (s8 != null && !s8.equals("-g:none"))54 error("main.conflicting.options", s8, "-g:none");55 s8 = "-g:none";56 i &= 0xffffefff;57 i &= 0xffffdfff;58 i &= 0xfffbffff;59 continue;60 }61 if (as[j].startsWith("-g:"))62 {63 if (s8 != null && !s8.equals(as[j]))64 error("main.conflicting.options", s8, as[j]);65 s8 =as[j];66 String s10 = as[j].substring("-g:".length());67 i &= 0xffffefff;68 i &= 0xffffdfff;69 i &= 0xfffbffff;70 do
71 {72 do
73 {74 if (s10.startsWith("lines"))75 {76 i |= 0x1000;77 s10 = s10.substring("lines".length());78 } else
79 if (s10.startsWith("vars"))80 {81 i |= 0x2000;82 s10 = s10.substring("vars".length());83 } else
84 if (s10.startsWith("source"))85 {86 i |= 0x40000;87 s10 = s10.substring("source".length());88 } else
89 {90 error("main.bad.debug.option", as[j]);91 usage_error();92 return false;93 }94 if (s10.length() == 0)95 continuelabel0;96 } while (!s10.startsWith(","));97 s10 = s10.substring(",".length());98 } while (true);99 }100 if (as[j].equals("-O"))101 {102 if (s9 != null && !s9.equals("-O"))103 error("main.conflicting.options", s9, "-O");104 s9 = "-O";105 continue;106 }107 if (as[j].equals("-nowarn"))108 {109 i &= -5;110 continue;111 }112 if (as[j].equals("-deprecation"))113 {114 i |= 0x200;115 continue;116 }117 if (as[j].equals("-verbose"))118 {119 i |= 1;120 continue;121 }122 if (as[j].equals("-nowrite"))123 {124 flag1 = true;125 continue;126 }127 if (as[j].equals("-classpath"))128 {129 if (j + 1 
135 {136 error("main.option.requires.argument", "-classpath");137 usage_error();138 return false;139 }140 continue;141 }142 if (as[j].equals("-sourcepath"))143 {144 if (j + 1 
150 {151 error("main.option.requires.argument", "-sourcepath");152 usage_error();153 return false;154 }155 continue;156 }157 if (as[j].equals("-sysclasspath"))158 {159 if (j + 1 
165 {166 error("main.option.requires.argument", "-sysclasspath");167 usage_error();168 return false;169 }170 continue;171 }172 if (as[j].equals("-bootclasspath"))173 {174 if (j + 1 
180 {181 error("main.option.requires.argument", "-bootclasspath");182 usage_error();183 return false;184 }185 continue;186 }187 if (as[j].equals("-extdirs"))188 {189 if (j + 1 
195 {196 error("main.option.requires.argument", "-extdirs");197 usage_error();198 return false;199 }200 continue;201 }202 if (as[j].equals("-encoding"))203 {204 if (j + 1 
210 {211 error("main.option.requires.argument", "-encoding");212 usage_error();213 return false;214 }215 continue;216 }217 if (as[j].equals("-target"))218 {219 if (j + 1 
226 {227 if (k >=releases.length)228 break;229 if(releases[k].equals(s4))230 {231 word0 =majorVersions[k];232 word1 =minorVersions[k];233 break;234 }235 k++;236 } while (true);237 if (k ==releases.length)238 {239 error("main.unknown.release", s4);240 usage_error();241 return false;242 }243 } else
244 {245 error("main.option.requires.argument", "-target");246 usage_error();247 return false;248 }249 continue;250 }251 if (as[j].equals("-d"))252 {253 if (j + 1 
265 {266 error("main.option.requires.argument", "-d");267 usage_error();268 return false;269 }270 continue;271 }272 if(as[j].equals(s5))273 {274 i |= 0x40;275 i &= 0xffffbfff;276 i &= 0xffff7fff;277 continue;278 }279 if (as[j].startsWith(s6) && as[j].length() >s6.length())280 {281 file1 = newFile(as[j].substring(s6.length()));282 i &= 0xffffbfff;283 i &= 0xffff7fff;284 i |= 0x40;285 i |= 0x80;286 continue;287 }288 if (as[j].equals("-XO"))289 {290 if (s9 != null && !s9.equals("-XO"))291 error("main.conflicting.options", s9, "-XO");292 s9 = "-XO";293 i |= 0x4000;294 continue;295 }296 if (as[j].equals("-Xinterclass"))297 {298 if (s9 != null && !s9.equals("-Xinterclass"))299 error("main.conflicting.options", s9, "-Xinterclass");300 s9 = "-Xinterclass";301 i |= 0x4000;302 i |= 0x8000;303 i |= 0x20;304 continue;305 }306 if (as[j].equals("-Xdepend"))307 {308 i |= 0x20;309 continue;310 }311 if (as[j].equals("-Xdebug"))312 {313 i |= 2;314 continue;315 }316 if (as[j].equals("-xdepend") || as[j].equals("-Xjws"))317 {318 i |= 0x400;319 if (out ==System.err)320 out =System.out;321 continue;322 }323 if (as[j].equals("-Xstrictdefault"))324 {325 i |= 0x20000;326 continue;327 }328 if (as[j].equals("-Xverbosepath"))329 {330 flag = true;331 continue;332 }333 if (as[j].equals("-Xstdout"))334 {335 out =System.out;336 continue;337 }338 if (as[j].equals("-X"))339 {340 error("main.unsupported.usage");341 return false;342 }343 if (as[j].equals("-Xversion1.2"))344 {345 i |= 0x800;346 continue;347 }348 if (as[j].endsWith(".java"))349 {350 vector.addElement(as[j]);351 } else
352 {353 error("main.no.such.option", as[j]);354 usage_error();355 return false;356 }357 }358
359 if (vector.size() == 0 || exitStatus == 2)360 {361 usage_error();362 return false;363 }364 BatchEnvironment batchenvironment =BatchEnvironment.create(out, s, s1, s2, s3);365 if(flag)366 output(getText("main.path.msg", batchenvironment.sourcePath.toString(), batchenvironment.binaryPath.toString()));367 batchenvironment.flags |=i;368 batchenvironment.majorVersion =word0;369 batchenvironment.minorVersion =word1;370 batchenvironment.covFile =file1;371 batchenvironment.setCharacterEncoding(s7);372 String s11 = getText("main.no.memory");373 String s12 = getText("main.stack.overflow");374 batchenvironment.error(0L, "warn.class.is.deprecated", "sun.tools.javac.Main");375 try
376 {377 for (Enumeration enumeration =vector.elements(); enumeration.hasMoreElements();)378 {379 File file2 = newFile((String)enumeration.nextElement());380 try
381 {382 batchenvironment.parseFile(newClassFile(file2));383 }384 catch(FileNotFoundException filenotfoundexception1)385 {386 batchenvironment.error(0L, "cant.read", file2.getPath());387 exitStatus = 2;388 }389 }390
391 Object obj1 =batchenvironment.getClasses();392 do
393 {394 if (!((Enumeration) (obj1)).hasMoreElements())395 break;396 ClassDeclaration classdeclaration =(ClassDeclaration)((Enumeration) (obj1)).nextElement();397 if (classdeclaration.getStatus() == 4 && !classdeclaration.getClassDefinition().isLocal())398 try
399 {400 classdeclaration.getClassDefinition(batchenvironment);401 }402 catch(ClassNotFound classnotfound) { }403 } while (true);404 obj1 = new ByteArrayOutputStream(4096);405 booleanflag2;406 do
407 {408 flag2 = true;409 batchenvironment.flushErrors();410 Enumeration enumeration1 =batchenvironment.getClasses();411 do
412 {413 if (!enumeration1.hasMoreElements())414 break;415 ClassDeclaration classdeclaration1 =(ClassDeclaration)enumeration1.nextElement();416 switch(classdeclaration1.getStatus())417 {418 case 1: //'\001'
419 case 2: //'\002'
420 default:421 break;422
423 case 0: //'\0'
424 if (!batchenvironment.dependencies())425 continue;426 //fall through
427
428 case 3: //'\003'
429 batchenvironment.dtEvent((new StringBuilder()).append("Main.compile (SOURCE): loading, ").append(classdeclaration1).toString());430 flag2 = false;431 batchenvironment.loadDefinition(classdeclaration1);432 if (classdeclaration1.getStatus() != 4)433 {434 batchenvironment.dtEvent((new StringBuilder()).append("Main.compile (SOURCE): not parsed, ").append(classdeclaration1).toString());435 continue;436 }437 //fall through
438
439 case 4: //'\004'
440 if(classdeclaration1.getClassDefinition().isInsideLocal())441 {442 batchenvironment.dtEvent((new StringBuilder()).append("Main.compile (PARSED): skipping local class, ").append(classdeclaration1).toString());443 continue;444 }445 flag2 = false;446 batchenvironment.dtEvent((new StringBuilder()).append("Main.compile (PARSED): checking, ").append(classdeclaration1).toString());447 SourceClass sourceclass =(SourceClass)classdeclaration1.getClassDefinition(batchenvironment);448 sourceclass.check(batchenvironment);449 classdeclaration1.setDefinition(sourceclass, 5);450 //fall through
451
452 case 5: //'\005'
453 SourceClass sourceclass1 =(SourceClass)classdeclaration1.getClassDefinition(batchenvironment);454 if(sourceclass1.getError())455 {456 batchenvironment.dtEvent((new StringBuilder()).append("Main.compile (CHECKED): bailing out on error, ").append(classdeclaration1).toString());457 classdeclaration1.setDefinition(sourceclass1, 6);458 continue;459 }460 flag2 = false;461 ((ByteArrayOutputStream) (obj1)).reset();462 batchenvironment.dtEvent((new StringBuilder()).append("Main.compile (CHECKED): compiling, ").append(classdeclaration1).toString());463 sourceclass1.compile(((OutputStream) (obj1)));464 classdeclaration1.setDefinition(sourceclass1, 6);465 sourceclass1.cleanup(batchenvironment);466 if (sourceclass1.getNestError() ||flag1)467 continue;468 String s14 = classdeclaration1.getName().getQualifier().toString().replace('.', File.separatorChar);469 String s15 = (new StringBuilder()).append(classdeclaration1.getName().getFlatName().toString().replace('.', '$')).append(".class").toString();470 File file3;471 if (file != null)472 {473 if (s14.length() > 0)474 {475 file3 = newFile(file, s14);476 if (!file3.exists())477 file3.mkdirs();478 file3 = newFile(file3, s15);479 } else
480 {481 file3 = newFile(file, s15);482 }483 } else
484 {485 ClassFile classfile =(ClassFile)sourceclass1.getSource();486 if(classfile.isZipped())487 {488 batchenvironment.error(0L, "cant.write", classfile.getPath());489 exitStatus = 2;490 continue;491 }492 file3 = newFile(classfile.getPath());493 file3 = newFile(file3.getParent(), s15);494 }495 try
496 {497 FileOutputStream fileoutputstream = newFileOutputStream(file3.getPath());498 ((ByteArrayOutputStream) (obj1)).writeTo(fileoutputstream);499 fileoutputstream.close();500 if(batchenvironment.verbose())501 output(getText("main.wrote", file3.getPath()));502 }503 catch(IOException ioexception1)504 {505 batchenvironment.error(0L, "cant.write", file3.getPath());506 exitStatus = 2;507 }508 if(batchenvironment.print_dependencies())509 sourceclass1.printClassDependencies(batchenvironment);510 break;511 }512 } while (true);513 } while (!flag2);514 }515 catch(OutOfMemoryError outofmemoryerror)516 {517 batchenvironment.output(s11);518 exitStatus = 3;519 return false;520 }521 catch(StackOverflowError stackoverflowerror)522 {523 batchenvironment.output(s12);524 exitStatus = 3;525 return false;526 }527 catch(Error error1)528 {529 if (batchenvironment.nerrors == 0 ||batchenvironment.dump())530 {531 error1.printStackTrace();532 batchenvironment.error(0L, "fatal.error");533 exitStatus = 4;534 }535 }536 catch(Exception exception)537 {538 if (batchenvironment.nerrors == 0 ||batchenvironment.dump())539 {540 exception.printStackTrace();541 batchenvironment.error(0L, "fatal.exception");542 exitStatus = 4;543 }544 }545 int i1 =batchenvironment.deprecationFiles.size();546 if (i1 > 0 &&batchenvironment.warnings())547 {548 int j1 =batchenvironment.ndeprecations;549 Object obj2 = batchenvironment.deprecationFiles.elementAt(0);550 if(batchenvironment.deprecation())551 {552 if (i1 > 1)553 batchenvironment.error(0L, "warn.note.deprecations", new Integer(i1), newInteger(j1));554 else
555 batchenvironment.error(0L, "warn.note.1deprecation", obj2, newInteger(j1));556 } else
557 if (i1 > 1)558 batchenvironment.error(0L, "warn.note.deprecations.silent", new Integer(i1), newInteger(j1));559 else
560 batchenvironment.error(0L, "warn.note.1deprecation.silent", obj2, newInteger(j1));561 }562 batchenvironment.flushErrors();563 batchenvironment.shutdown();564 boolean flag3 = true;565 if (batchenvironment.nerrors > 0)566 {567 String s13 = "";568 if (batchenvironment.nerrors > 1)569 s13 = getText("main.errors", batchenvironment.nerrors);570 else
571 s13 = getText("main.1error");572 if (batchenvironment.nwarnings > 0)573 if (batchenvironment.nwarnings > 1)574 s13 = (new StringBuilder()).append(s13).append(", ").append(getText("main.warnings", batchenvironment.nwarnings)).toString();575 else
576 s13 = (new StringBuilder()).append(s13).append(", ").append(getText("main.1warning")).toString();577 output(s13);578 if (exitStatus == 0)579 exitStatus = 1;580 flag3 = false;581 } else
582 if (batchenvironment.nwarnings > 0)583 if (batchenvironment.nwarnings > 1)584 output(getText("main.warnings", batchenvironment.nwarnings));585 else
586 output(getText("main.1warning"));587 if(batchenvironment.covdata())588 {589 Assembler assembler = newAssembler();590 assembler.GenJCov(batchenvironment);591 }592 if(batchenvironment.verbose())593 {594 l = System.currentTimeMillis() -l;595 output(getText("main.done_in", Long.toString(l)));596 }597 returnflag3;598 }

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