Decompiler for Java 1.5+

Hi,

Is there any decompiler for latest java version. i.e to decompile java 1.5 features like Generic Types, Enum etc.

Thanks
Kumaran

Bad idea dude.

From the java license file

3. RESTRICTIONS. Software is confidential and copyrighted.
Title to Software and all associated intellectual property
rights is retained by Sun and/or its licensors. Unless
enforcement is prohibited by applicable law, you may not
modify, decompile, or reverse engineer Software.

Are you aware that Sun gives away the source code too?
Check out your java installation directory for a file called src.zip. You are legally allowed to view that source code. If what you want is not in there, then its illegal.

I think what Kumaran means is that all the freely available decompilers (like JAD and JODE) do not support those Java 5 features, so the code they emit is pretty far from the original source code. I've had good luck adding support for generics to JODE (it's not all that hard), but supporting enums would be rather more complicated.

Maneesh Godbole wrote:Bad idea dude.

From the java license file

But you can still decompile your own code, or code from others that do allow decompiling.

As for the answer: you can't. The reason is quite clear: the compiler erases this information.

For instance:

Enums get compiled into a class that extends java.lang.Enum. All enum constants are public static final fields of the same type; the constructors get two fields added (ordinal and name) which get filled in by the compiler. values() returns a clone() of a private static array called $VALUES.

Generic types get completely erased at compile time, and converted in explicit casts where needed (search for type erasure for more information).

For-each loops get turned into simple loops using an Iterator or array index.

I've decompiled classes often enough (out of interest) to know

Ulf Dittmer wrote:I've had good luck adding support for generics to JODE (it's not all that hard), but supporting enums would be rather more complicated.

How did you do that? Using the type objects are cast to? That's the only remaining reference to the generic type after compiling, as far as I know.
As for enums, those should also not be that hard if you follow the rules I mentioned in my previous post. Simply create some enums, decompile them and see how its done. You can simply tell it's an enum because it extends java.lang.Enum ;)

Hello..
I understand the license. I dont want to decompile Sun's java code. I know that they distribute it.

I need to decompile some other sample class file. which i downloaded from Internet.

Thanks
Kumaran

Rob Prime wrote:

Ulf Dittmer wrote:I've had good luck adding support for generics to JODE (it's not all that hard), but supporting enums would be rather more complicated.

How did you do that? Using the type objects are cast to? That's the only remaining reference to the generic type after compiling, as far as I know.

Let me qualify that: I added support for restoring the generics information in class and method signatures, as well as field declarations, not within the actual code. That information is mostly stripped away as you say. But the classfile attributes contain the information for the class itself, its fields and methods.

As for enums, those should also not be that hard if you follow the rules I mentioned in my previous post. Simply create some enums, decompile them and see how its done. You can simply tell it's an enum because it extends java.lang.Enum ;)

I don't recall all the details, but it seemed more involved than that. But it wasn't that important to me compared to generics) so I didn't pursue it.

Thanks Ulf and Rob, I was looking for these kind of information like why we are not able to decompile completely... ;-)

I found the example Enums I used for analyzing the bytecode that gets generated. For example, this simple Enum:
enum Grade { A, B, C, D, F, INCOMPLETE; }
is turned into:
static final class Grade extends Enum { public static final Grade A = new Grade("A", 0); public static final Grade B = new Grade("B", 1); public static final Grade C = new Grade("C", 2); public static final Grade D = new Grade("D", 3); public static final Grade F = new Grade("F", 4); public static final Grade INCOMPLETE = new Grade("INCOMPLETE", 5); /*synthetic*/ private static final Grade[] $VALUES = { A, B, C, D, F, INCOMPLETE }; public static final Grade[] values() { return (Grade[]) $VALUES.clone(); } public static Grade valueOf(String string) { return (Grade) Enum.valueOf(Grade.class, string); } private Grade(String string, int i) { super(string, i); } }
That's a fair amount of code to analyze until you can conclude that it's a bare bones Enum. Something slightly more complicated:
enum Size { Small(0.8), Medium(1.0), Large(1.2); private double pricingFactor; Size (double p) { pricingFactor = p; } public double getPricingFactor() { return pricingFactor; } }
is turned into
static final class Size extends Enum { public static final Size Small = new Size("Small", 0, 0.8); public static final Size Medium = new Size("Medium", 1, 1.0); public static final Size Large = new Size("Large", 2, 1.2); private double pricingFactor; /*synthetic*/ private static final Size[] $VALUES = { Small, Medium, Large }; public static final Size[] values() { return (Size[]) $VALUES.clone(); } public static Size valueOf(String string) { return (Size) Enum.valueOf(Size.class, string); } private Size(String string, int i, double d) { super(string, i); pricingFactor = d; } public double getPricingFactor() { return pricingFactor; } }
So you'd have to analyze the Size constructor calls to get the values. Certainly not rocket science, but not particularly fun stuff to code, either...

It becomes even harder when enum constants override methods. A good example is java.util.concurrent.TimeUnit - a 332 line source file (and that's including lots of comments) turns into a 479 line source file after decompiling - without comments. That's because every one of the enum constants has its own anonymous class that overrides 9 methods.