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Questions tagged [jvm-bytecode]

Questions about the JVM .class bytecode format or instruction set.

188 questions
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Tool to read and display Java .class versions

Do any of you know of a tool that will search for .class files and then display their compiled versions? I know you can look at them individually in a hex editor but I have a lot of class files to look over (something in my giant application is…
SCdF
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Kotlin Bytecode - How to analyze in IntelliJ IDEA?

I want to see the compiled bytecode so I can learn more about how it works under the cover. I'm using IntelliJ IDEA 15 but can't find a way to see the bytecode. What am I missing?
CaseyB
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42
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3 answers

Dynamic Java Bytecode Manipulation Framework Comparison

There are some frameworks out there for dynamic bytecode generation, manipulation and weaving (BCEL, CGLIB, javassist, ASM, MPS). I want to learn about them, but since I don't have much time to know all the details about all of them, I would like to…
Victor Stafusa - BozoNaCadeia
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25
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2 answers

Null or empty lambda as default value

Which solution is better? Using a nullable lambda or passing an empty lambda as a default parameter? Would kotlin somehow optimize empty lambda, or create a new instance that does nothing? class Test1(val action: () -> Unit = {}) Unfortunately, I do…
Paweł Byszewski
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16
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1 answer

Java bytecode decompiler in IntelliJIDEA for Scala

I'm using IntellijIDEA Ultimate Edition. Browsing .class files that compiled from java source code is easy: I can just double-click on .class file and IDEA will decompile it. However, with .class files that were compiled from scala source code it's…
Dmitry K
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13
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3 answers

java.lang.VerifyError: Stack map does not match the one at exception handler

Faced this java.lang.VerifyError with code snippet as below during JVM loading bytecode. try{ ----- } catch (NumberFormatException|CalculationException e) { } Here CalculationException is custom exception which extends java.lang.RuntimeException,…
tarunk
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13
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1 answer

Kotlin inlined extension property

I know inline keyword means to avoid the call overhead calling a funtion. But I can't figure out what inline a extension property work for? Let say we have two extension property named foo and another with is inlined named bar val Any.foo : Long …
crgarridos
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11
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3 answers

Reversed if condition in java bytecode

Consider simple example private static String isPositive(int val) { if (val > 0) { return "yes"; } else { return "no"; } } Here it's pretty straightforward: if val > 0 return yes else return no. But after compilation, in…
esin88
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10
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1 answer

Status of JSR/RET in JVM spec

There are some parts of the JVM specification which suggest that the operations JSR (Jump SubRoutine), JSR_W (Jump SubRoutine Wide) and RET (RETurn from subroutine) may be used only up to class file version 50.0 (JDK 1.6): 3.13 Compiling…
MvG
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9
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4 answers

Bytecode transforming record class to be mutable

I just saw that EBean does bytecode transformation of record class files in a way that feels odd to me and I seek an answer about whether this is legal from a JVM point of view. Apparently, it is possible to have a class file, where the class…
Christian Beikov
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9
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1 answer

Javap output: difference static {} and public {}

I have two example class files, one from an example Java app and one from an example C app (compiled to bytecode using LLJVM). Looking at their outputs, I can see through javap -c -p that for initializing the (static) fields, the Java app shows the…
Sven
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9
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1 answer

How to create a dynamic proxy using ByteBuddy

In Java it is possible to create dynamic proxies using an implementation of InvocationHandler. Despite JVM optimizations, using reflection will always have some overhead invoking a method. To try to solve this problem, I tried to use ByteBuddy to…
Carlos Melo
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7
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3 answers

Why does java bytecode "store" often followed by "load"?

When I read jvm bytecode which from some small java function, I found that when a new local variable is caculated on the operand stack, assuming that it will be stored in the local variable table, but usually it will be loaded to the operand stack…
Q_SJ
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7
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Variable 'final' modifier lost in Bytecode?

Analyzing the bytecode of this simple class, I have come to the conclusion that the compiler doesn't retain any information about a local variable being final. This seems weird though, since I believe the HotSpot compiler could actually use this…
Clashsoft
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7
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Why is there no ICMP instruction?

As some of you might know, we have a ton of opcodes for comparing different types of primitive…
Clashsoft
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