How to read the metadata for the mnemonics produced by disassembled Java Bytecode? -

-

i've never used javap before. explain "code" means in example? shows threes time. mean in context of mnemonics follow on lines below it? indicate there stack frame or something?:

compiled "docfooter.java" public class docfooter extends java.applet.applet {   java.lang.string date;    java.lang.string email;    public docfooter();     code:        0: aload_0               1: invokespecial #1                  // method java/applet/applet."<init>":()v        4: return            public void init();     code:        0: aload_0               1: sipush        500        4: bipush        100        6: invokevirtual #2                  // method resize:(ii)v        9: aload_0              10: aload_0              11: ldc           #3                  // string last_updated       13: invokevirtual #4                  // method getparameter:(ljava/lang/string;)ljava/lang/string;       16: putfield      #5                  // field date:ljava/lang/string;       19: aload_0              20: aload_0              21: ldc           #6                  // string email       23: invokevirtual #4                  // method getparameter:(ljava/lang/string;)ljava/lang/string;       26: putfield      #7                  // field email:ljava/lang/string;       29: return            public void paint(java.awt.graphics);     code:        0: aload_1               1: new           #8                  // class java/lang/stringbuilder        4: dup                   5: invokespecial #9                  // method java/lang/stringbuilder."<init>":()v        8: aload_0               9: getfield      #5                  // field date:ljava/lang/string;       12: invokevirtual #10                 // method java/lang/stringbuilder.append:(ljava/lang/string;)ljava/lang/stringbuilder;       15: ldc           #11                 // string         17: invokevirtual #10                 // method java/lang/stringbuilder.append:(ljava/lang/string;)ljava/lang/stringbuilder;       20: invokevirtual #12                 // method java/lang/stringbuilder.tostring:()ljava/lang/string;       23: bipush        100       25: bipush        15       27: invokevirtual #13                 // method java/awt/graphics.drawstring:(ljava/lang/string;ii)v       30: aload_1              31: aload_0              32: getfield      #7                  // field email:ljava/lang/string;       35: sipush        290       38: bipush        15       40: invokevirtual #13                 // method java/awt/graphics.drawstring:(ljava/lang/string;ii)v       43: return         }

i looked through spec jvm , didn't find explaining "code:", if turns out overlooked pleased post link section. thanks.

javap tool designed java programmers debug code. not designed consumed tools , there no formal specification output. can , change version version.

that being said, if understand jvm specification , classfile format, it's easy understand output of javap.

also note javap tries make things more java-like, hides or obscures of details of bytecode. example, outputs java style method signatures, doesn't necessary reflect in bytecode (and hides synthetic parameters).

if want see closer bytecode is, still human readable, i'd recommend krakatau disassembler (disclosure, wrote it). there lot of other tools viewing bytecode out there, , they're better javap (it's not hard better javap).

furthermore, line numbers (0:),

the line number offset of instruction in bytecode. starts @ 0, , instructions either 1 or 3 bytes. see jvm spec details.

what different sections mean (public void init() followed code: on next line), , #[number] , comments mean?

that shows each method in class, javap-mangled java style method signature. followed textual representation of each instruction in method's bytecode. again, see jvm spec details.


Comments

Post a Comment

Popular posts from this blog

yii2 - Yii 2 Running a Cron in the basic template -

-
i have seen instructions on running cron in advanced template, cant figure out how on basic template. have following controller in basic controllers folder. <?php namespace app\controllers; use yii\console\controller; /** * cron controller */ class croncontroller extends controller { public function actionindex() { echo "cron service runnning"; } public function actionmail($to) { echo "sending mail " . $to; } } i have navigated root of application , tried these comands yii cron php yii cron im getting unknown comand "cron" i know old question failed find actual answer this. if @ code yii exec file you'll notice requires /common/config/aliases.php file console/config/main.php. can naturally change these or copy on these advanced template. hope solves problem wanting same thing.
Read more

asp.net - 'System.Web.HttpContext' does not contain a definition for 'GetOwinContext' Mystery -

-
i realize question might seem trivial some, it's these types of things find myself fighting quite bit , want make sense of despite seeming losing battle in .net (for me anyway). so, if following: using system.web; ... applicationuser user = system.web.httpcontext.getowincontext().getusermanager<applicationusermanager>().findbyid(system.web.httpcontext.user.identity.getuserid()); that produces error in title , red getowincontext() , error cannot resolve symbol 'getowincontext()' however, if following (remove system.web in front of httpcontext ), works expected (or @ least no errors): using system.web; ... applicationuser user = httpcontext.getowincontext().getusermanager<applicationusermanager>().findbyid(system.web.httpcontext.user.identity.getuserid()); however, if (same line that's working using system.web commented out): //using system.web; ... applicationuser user = httpcontext.getowincontext().getusermana...
Read more

mercurial graft feature, can it copy? -

-
there new feature in mercurial 3, called 'graft' (graft local). job of moving change-set different branch. is there way "copy" change-set branch? i interested in in moving stuff qa branch production branch, still need code reside in qa. want copy. found , have tried few things, maybe it'll become clear more tinkering , reading... does have better way of 'cherry picking' change-sets move cross branch (or trunk)??? graft copies changesets, doesn't move them. hg graft (emphasis mine): this command uses mercurial's merge logic copy individual changes other branches without merging branches in history graph. known 'backporting' or 'cherry-picking' . default, graft copy user, date, , description source changesets.
Read more