Is it possible to view a Java class files bytecode

Question

I am working on a bytecode manipulation/generation in Java and I was just wondering if there is an easy way I could check the bytecode. I do not want to decompile the file, I would like to actually look at the compiled bytecode. I do not need to edit it. Any links or programs for doing this would be acceptable answers.

You can normally do it directly from within your IDE. Maybe with a little help from a plugin. — maba, May 27 '13 at 13:54
I think `javap` is what you are looking for. A command that comes with the JDK. — Marko Topolnik, May 27 '13 at 13:54
@Popgalop `javap -v` shows the bytecode - see my answer below. — Oak, May 27 '13 at 14:01

score 48 · Answer 1 · answered May 27 '13 at 14:12

48

Since you wanted to be guided to some program that can easily show you the byte code then my suggestion is to use IntelliJ IDEA since it has built-in support for viewing byte code.

Here's an example how to do it (it can also be mapped to some keys of your choice):

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It is very easy, and it can surely be done in eclipse or NetBeans as well.

answered May 27 '13 at 14:12

maba

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where's line numbers? What are L0,L1.. mean ???? – voipp Aug 23 '15 at 15:57
Is this also available in Android studio? At least for classes compield for the JVM (like local Unit Tests etc). – Igor Čordaš Sep 16 '16 at 12:03
@PSIXO I don't know, I only use IntelliJ as-is. – maba Sep 16 '16 at 12:07
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note that this requires the _ByteCode Viewer_ plugin – Ciprian Tomoiagă May 12 '17 at 15:33
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@voipp `LINENUMBER 10 L2` means that the code on line number 10 is located at label `L2`. So `L0`, `L1` etc are labels, i.e. jump points in your program. In bytecode there are no functions or loops, there are only jumps (which can be conditional). So the whole program is a bunch of `IF this GO there_1; IF that GO there_2` – Ciprian Tomoiagă May 12 '17 at 15:39
`javap -c` outputs something completely different, something much simpler. Is there a way to view that as well? – Nearoo Mar 08 '18 at 17:16

score 6 · Answer 2 · answered May 27 '13 at 13:57

6

Not sure what exactly you need, but apart from javap, which is a command-line tool for displaying the bytecode, you can take a look at javassist, asm and cglib - they allow you to parse the bytecode with java code.

answered May 27 '13 at 13:57

Bozho

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score 2 · Answer 3 · answered May 27 '13 at 13:56

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The javap command-line tool, which is bundled with Oracle's JDK, gives a detailed textual dump of .class files along with the constant pool and all functions' bytecode content. Just run it with -v to get a full dump.

answered May 27 '13 at 13:56

Oak

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but i want to see what the compiler reads when it reads the file so that i can create my own synthetic classes. – Popgalop May 27 '13 at 22:23
@Popgalop what the compiler reads in is the actual bytecode, which is not a textual format. I guess you could open it in a hex editor and use [this reference](http://docs.oracle.com/javase/specs/jvms/se5.0/html/ClassFile.doc.html) to parse it by yourself, but if you want a human-readable dump, `javap -v` is the answer. – Oak May 28 '13 at 07:15

score 2 · Accepted Answer · answered May 28 '13 at 18:55

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I've been working on a decompiler that has a color-coded bytecode output mode (which I find far more readable than javap). It can also output Java code or an intermediate 'bytecode AST'.

answered May 28 '13 at 18:55

Mike Strobel

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Is it possible to view a Java class files bytecode

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