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  • Book (or resource) on Java bytecode

    - by Andrea
    I am looking for some resources on the JVM bytecode. Ideally I would for a short book; something more than a blog post but not a 800 pages tome. If it is relevant, I am a Scala developer, not a Java one, although I know Java just fine. I would like something that allowed me to read JVM bytecode and answer questions such as: Why does the bytecode has to know about high level construct such as classes? Are subtyping relations still visible in bytecode? How does type erasure work exactly? How do Oracle and Dalvik bytecode differ, and what consequences does this have for, say, developing Android apps with Scala? How does the JVM manage the stack, and why exactly this creates issues with tail call elimination? and so on.

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  • Stand-alone Bytecode Verifier

    - by HH
    In my bytecode instrumentation project, I stumble frequently on VerifyErrors. However, the default java Verifier gives little information on which instruction resulted in the error (it only gives the method and a small message). Is there any stand-alone bytecode verifier which provides with a little more advanced help in locating the error, at least the precise instruction location? Thank you.

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  • How are Scala traits compiled into Java bytecode?

    - by Justin Ardini
    I have played around with Scala for a while now, and I know that traits can act as the Scala equivalent of both interfaces and abstract classes. Recently I've been wondering how exactly traits are compiled into Java bytecode. I found some short explanations that stated traits are compiled exactly like Java interfaces when possible, and interfaces with an additional class otherwise. I still don't understand, however, how Scala achieves class linearization, a feature not available in Java. Could anyone explain or provide a good source explains how traits compile to Java bytecode?

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  • Bytecode and Objects

    - by HH
    Hey everyone, I am working on a bytecode instrumentation project. Currently when handling objects, the verifier throws an error most of the time. So I would like to get things clear concerning rules with objects (I read the JVMS but couldn't find the answer I was looking for): I am instrumenting the NEW instruction: original bytecode NEW <MyClass> DUP INVOKESPECIAL <MyClass.<init>> after instrumentation NEW <MyClass> DUP INVOKESTATIC <Profiler.handleNEW> DUP INVOKESPECIAL <MyClass.<init>> Note that I added a call to Profiler.handleNEW() which takes as argument an object reference (the newly created object). The piece of code above throws a VerificationError. While if I don't add the INVOKESTATIC (leaving only the DUP), it doesn't. So what is the rule that I'm violating? I can duplicate an uninitialized reference but I can't pass it as parameter? I would appreciate any help. Thank you

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  • running jython bytecode using java

    - by noamtm
    It looks like I'm missing something. When using Jython to run my Python code in Java, Java bytecode files are generated (test.py - [email protected]). Can I run these classes directly using java? In other words, I want to make this: $ java test@py [additional cp args] work. The intent: writing Python code and not having to give away source code.

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  • Which are the fundamental stack manipulation operations?

    - by Aadit M Shah
    I'm creating a stack oriented virtual machine, and so I started learning Forth for a general understanding about how it would work. Then I shortlisted the essential stack manipulation operations I would need to implement in my virtual machine: drop ( a -- ) dup ( a -- a a ) swap ( a b -- b a ) rot ( a b c -- b c a ) I believe that the following four stack manipulation operations can be used to simulate any other stack manipulation operation. For example: nip ( a b -- b ) swap drop -rot ( a b c -- c a b ) rot rot tuck ( a b -- b a b ) dup -rot over ( a b -- a b a ) swap tuck That being said however I wanted to know whether I have listed all the fundamental stack manipulation operations necessary to manipulate the stack in any possible way. Are there any more fundamental stack manipulation operations I would need to implement, without which my virtual machine wouldn't be Turing complete?

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  • Types in Bytecode

    - by HH
    Hey everyone, I've been working for some time on (Java) Bytecode, however, it had never occurred to me to ask why are some instructions typed? I understand that in an ADD operation, we need to distinguish between an integer addition and a FP addition (that's why we have IADD and FADD). However, why do we need to distinguish between ISTORE and FSTORE? They both involve the exact same operation, which is moving 32 bits from the stack to a local variable position? The only answer I can think of is for type-safety, to prevent this: (ILOAD, ILOAD, FADD). However, I believe that type-safety is already enforced at the Java language level. OK, the Class file format is not directly coupled with Java, so is this a way to enforce type-safety for languages that do not support it? Any thought? Thank you.

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  • Pros and Cons of programming languages for XML & string manipulation

    - by aepheus
    I don't mean this to be opinionated. What are serious pros/cons of various server-side languages in regards to creating/modifying xml. I'm currently researching new platform/language direction and we deal with a lot of xml. We also do a lot of string manipulation, what advantages/disadvantages do different languages have in regards to string manipulation. I'm thinking along the lines of regular expression searching and replacing.

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  • String manipulation of type String substitution in mathematical expression

    - by Peterstone
    Imagine something like exp(49/200)+(x-49/200) I want to pass as argument of the function "roundn" whatever operation that is not a addtion or a subtraction So my expresion became roundn(exp(roundn(49/200,n)),n)+(x - roundn(49/200,n) Well the expression I want to manipulate is this: exp(49/200)+exp(49/200)*(x-49/200)+1/2*exp(49/200)*(x-49/200)^2+1/6*exp(49/200)*(x- 49/200)^3+1/24*exp(49/200)*(x-49/200)^4+1/120*exp(49/200)*(x-49/200)^5+1/720*exp(49/200)*(x-49/200)^6+1/5040*exp(49/200)*(x-49/200)^7+1/40320*exp(49/200)*(x-49/200)^8+1/362880*exp(49/200)*(x-49/200)^9+1/3628800*exp(49/200)*(x-49/200)^10+1/39916800*exp(49/200)*(x-49/200)^11 I´m looking for a method (That include whatever program) not based in lenguage programming, as much batch or somithing like that... Thank you!

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  • Converting ANTLR AST to Java bytecode using ASM

    - by Nick
    I am currently trying to write my own compiler, targeting the JVM. I have completed the parsing step using Java classes generated by ANTLR, and have an AST of the source code to work from (An ANTLR "CommonTree", specifically). I am using ASM to simplify the generating of the bytecode. Could anyone give a broad overview of how to convert this AST to bytecode? My current strategy is to explore down the tree, generating different code depending on the current node (using "Tree.getType()"). The problem is that I can only recognise tokens from my lexer this way, rather than more complex patterns from the parser. Is there something I am missing, or am I simply approaching this wrong? Thanks in advance :)

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  • Is there a way in .NET to access the bytecode/IL/CLR that is currently running?

    - by Alix
    Hi. I'd like to have access to the bytecode that is currently running or about to run in order to detect certain instructions and take specific actions (depending the instructions). In short, I'd like to monitor the bytecode in order to add safety control. Is this possible? I know there are some AOP frameworks that notify you of specific events, like an access to a field or the invocation of a method, but I'd like to skip that extra layer and just look at all the bytecode myself, throughout the entire execution of the application. I've already looked at the following questions (...among many many others ;) ):     Preprocessing C# - Detecting Methods     What CLR/.NET bytecode tools exist? as well as several AOP frameworks (although not in great detail, since they don't seem to do quite what I need) and I'm familiar with Mono.Cecil. I appreciate alternative suggestions, but I don't want to introduce the overhead of an AOP framework when what I actually need is access to the bytecode, without all the stuff they add on top to make it more user-friendly (... admittedly very useful stuff when you don't want to go low-level). Thanks :)

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  • Classic string manipulation interview questions?

    - by user189364
    Hi, I am scheduled to have an onsite interview so I am preparing few basic questions. According to the company profile, they are big on string manipulation questions. So far I have manually coded these functions: String length, copy, concat, remove white space Reverse Anagrams Palindrome Please can some can give me a list of more classic string questions which I can practice before going there?

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  • Feedback on "market manipulation", a peripheral game mechanic for a satirical MMO

    - by BerndBrot
    This question asks for feedback on a specific game-mechanic. Since there is not one right feedback on a game mechanic, I tried to provide enough context and guidelines to still make it possible for users to rate answers and to accept an answer as the best answer (following these criteria from Writer.SE's meta website). Please comment if you have any suggestions on how I could improve the question in that regard. So, let's begin with the game itself and some of its elements which are relevant for this question. Context I'm working on a satirical, text-based multiplayer adventure and role-playing game set in modern-day London. The game resolves around the concept of sin and features a myriad of (venomous) allusions to all the things that go wrong in this world. Players can choose between character classes like bullshit artist (consultant), bankster, lawyer, mobster, celebrity, politician, etc. In order to complete the game, the player has to live so sinfully with regard to any of the seven deadly sins that a demon is willing to offer them a contract of sponsorship. On their quest to live a sinful live, characters explore more and more locations of modern-day London (on a GoogleMap), fight "monsters" like insurance sales agents or Jehovah's Witnesses, and complete quests, like building a PowerPoint presentation out of marketing buzz words or keeping up a number of substance abuse effects in order to progress on the gluttony path. Battles are turn based with both combatants having a deck of cards, with which they try to make their enemy give in to temptations of all sorts. Tempted enemies sometimes become contacts (an item drop mechanic), which can be exploited for various benefits, depending on their area of influence (finance, underworld, bureaucracy, etc.), level of influence, and kind of sway that the player has over them (bribed, seduced, threatened, etc.) Once a contract has been exploited, the player loses that contact. Most actions require turns. Turns are limited, but refill each day. Criteria A number of peripheral game mechanics are supposed to represent real world abuses and mischief in a humorous way integrate real world data and events to strengthen the feeling of relevance of the game's humor with regard to real world problems add fun ways of interacting with other players add ways for players to express themselves through game-play Market manipulation is one such peripheral game mechanic and should fulfill all of these goals. Market manipulation This is my initial design of the mechanic: Players can enter the London Stock Exchange (LSE) (without paying a turn) LSE displays the stock prices of a number of companies in industries like weapons or tobacco as well as some derivatives based on wheat and corn. The stock prices are calculated based on the actual stock prices of these companies and derivatives (in real time) any market manipulations that were conducted by the players any market corrections of the system Players can buy and sell shares with cash, a resource in the game, at current in-game market value (without paying a turn). Players can manipulate the market, i.e. let the price of a share either rise or fall, by some amount, over a certain period of time. Manipulating the market requires 1 turn A contact in the financial sector (see above). The higher the level of influence of the contact, the stronger the effect of the manipulation on the stock price, and/or the shorter it takes for the manipulation to manifest itself. Market manipulation also adds a crime to the player's record. (There are a multitude of ways to take care of that, but it is still another "cost" of market manipulations.) The system continuously corrects market manipulations by letting the in-game prices converge towards their real world counterparts at a rate of 2% of the difference between the two per hour. Because of this market correction mechanism, pushing up prices (and screwing down prices) becomes increasingly difficult the higher (lower) the price already is. Whenever food prices reach a certain level, in-game stories are posted about hunger catastrophes happening somewhere far, far away (maybe with links to real world news stories). Whenever a player sells a certain number of shares with a sufficiently high margin, they are mentioned in that day's in-game financial news. Since the number of stock options is very limited, players will inevitably collide in their efforts to manipulate the market in their favor. Hopefully, it will also be a fun side-arena for guilds and covenants to fight each other. Question(s) What do you think of this mechanism given the criteria for peripheral game mechanics that I specified for my game? Do you have any ideas how the mechanic could be improved with regard to these criteria (or otherwise)? Could it be improved to allow for more expressive game-play, or involve an allusion to some other real world madness (like short selling, leveraging, or some other banking magic)? Are there any game-theoretic problems with this mechanic, like maybe certain dominant individual strategies that, collectively, lead to every player profiting and thus eliminating the idea of market manipulation PVP? Also, if you like (or dislike) this question, feel free to participate in the discussion on GDSE meta: "Should we be more lax with regard to SE's question/answer format to make game design questions possible?"

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  • Powershell and some simple string manipulation

    - by Pat
    need some help with building a powershell script to help with some basic string manipulation. I know just enough powershell to get in trouble, but can't figure out the syntax or coding to make this work. I have a text file that looks like this - Here is your list of servers: server1 server2.domain.local server3 Total number of servers: 3 I need to take that text file and drop the first and last lines (Always first and last.) Then I need to take every other line and basically turn it into a CSV file. The final output should be a text file that looks like this - server1,server2.domain.local,server3 Any suggestions on where to start? Thanks!

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  • Bitwise operators versus .NET abstractions for bit manipulation in C# prespective

    - by Leron
    I'm trying to get basic skills in working with bits using C#.NET. I posted an example yesterday with a simple problem that needs bit manipulation which led me to the fact that there are two main approaches - using bitwise operators or using .NET abstractions such as BitArray (Please let me know if there are more build-in tools for working with bits other than BitArray in .NET and how to find more info for them if there are?). I understand that bitwise operators work faster but using BitArray is something much more easier for me, but one thing I really try to avoid is learning bad practices. Even though my personal preferences are for the .NET abstraction(s) I want to know which i actually better to learn and use in a real program. Thinking about it I'm tempted to think that .NET abstractions are not that bad at, after all there must be reason to be there and maybe being a beginner it's more natural to learn the abstraction and later on improve my skills with low level operations, but this is just random thoughts.

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  • String Manipulation in C

    - by baris_a
    Hi guys, I am helping my nephew for his C lab homework, it is a string manipulation assignment and applying Wang's algorithm. Here is the BNF representation for the input. <sequent> ::= <lhs> # <rhs> <lhs> ::= <formulalist>| e <rhs> ::= <formulalist>| e <formulalist> ::= <formula>|<formula> , <formulalist> <formula> ::= <letter>| - <formula>| (<formula><in?xop><formula>) <in?xop> ::= & | | | > <letter> ::= A | B | ... | Z What is the best practice to handle and parse this kind of input in C? How can I parse this structure without using struct? Thanks in advance.

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