Question

I have an assignment wherein I have to parse the field access flags of a java .class file.
The specification for a .class file can be found here: Class File Format (page 26 & 27 have the access flags and hex vals).

This is fine, I can do this no worries.
My issue is that there is a large number of combinations.

I know the public, private and protected are mutually exclusive, which reduces the combinations somewhat. Final and transient are also mutually exclusive. The rest however are not.

At the moment, I have a large switch statement to do the comparison. I read in the hex value of the access flag and then increment a counter, depending on if it is public, private or protected. This works fine, but it seems quite messy to just have every combination listed in a switch statement. i.e. public static, public final, public static final, etc.

I thought of doing modulo on the access flag and the appropriate hex value for public, private or protected, but public is 0x0001, so that won’t work.

Does anyone else have any ideas as to how I could reduce the amount of cases in my switch statement?

Answer 1

What is the problem? The specification says that it’s a bit flag, that means that you should look at a value as a binary number, and that you can test if a specific value is set by doing a bitwise AND.

E.g

/*
ACC_VOLATILE = 0x0040 = 10000000
ACC_PUBLIC   = 0x0001 = 00000001
Public and volatile is= 10000001
*/


publicCount += flag & ACC_PUBLIC > 0 ? 1 : 0;
volatileCount += flag & ACC_VOLATILE > 0 ? 1 : 0;