Decompiled Java class producing different output

Question

Out of curiosity I just decompiled below code using DJ Java Decompiler as well using CAVAJ Java Decompiler ( Java version is 1.7 ) here is the normal source code :

---

    byte a = 10;
    a = (byte) (a +1);

    byte b = 10;
    b = b++;

    byte c = 10;
    c +=c;

    System.out.printf("a=%d \t b=%d \t c=%d\n",a,b,c);

Which shows output as: a=11 b=10 c=20

---

---

And here is the decompiled one:

    byte a = 10;
    a++;
    byte b = 10;
    b++;
    b = b;
    byte c = 10;
    c += c;
    System.out.printf("a= %d \t b = %d \t c = %d\n", new Object[] {
        Byte.valueOf(a), Byte.valueOf(b), Byte.valueOf(c)
    });

Which when used as source code output as: a=11 b=11 c=20

---

To be more clear it has nothing to do with byte same thing happening for int as well and I even checked above codes in online compiler IDEONE and giving the same output as mine.

So, is the decompiler producing wrong code or is something else ??

Answer 1

I will give you short answer: yes, it seems, that the decompiler is producing wrong code. Because this one:

byte b = 10;
b = b++;

has strongly predicted behavior (b will not change).

UPD: Furthermore, no one of decompilers can give you 100% warranty of the correctness of generated decompiled code.

UPD-2: Are you sure, that you provide us actual version of your code? Because this one:

byte aa = 10;
a = (byte) (a +1);

of course is a mistake. It even will not compile :)

UPD-3 Well, I need to say, that Jad decompiler (Jad 1.5.8g for Windows 9x/NT/2000 on Intel platform) produces the same code:

    byte b = 10;
    b++;
    b = b;

...

    java.lang.System.out.printf("a=%d \t b=%d \t c=%d\n", new java.lang.Object[] {...

But this is not surprising: Cavaj Java decompiler uses Jad as its Java decompiling engine.

Conclusion: Consider this behavior as a feature/bug of Jad decompiler, which is far from a perfection.