Method Order in generated class file by javac

Question

With JDK7, the reflection API has changed and now the methods returned by getDeclaredMethods() are not returned in the order in which they are declared in the source file.

Now my question is, does the .class file generated by javac contains methods in the same order in which they were defined in the source file OR it can write methods in random order too?

Answer 1

Class.getDeclaredMethods API is clear about this "...The elements in the array returned are not sorted and are not in any particular order...". Most likely the reason of that is that javac is not obliged to generate methods in .class in any particular order.

Answer 2

The Binary Compatibility chapter of the Java Language Specification is explicit about the fact that reordering of elements in the class files is permitted:

[...] here is a list of some important binary compatible changes that the Java programming language supports:

• [...]

• Reordering the fields, methods, or constructors in an existing type declaration.

• [...]

• Reordering the list of direct superinterfaces of a class or interface.

That means that the order in which they appear in the .class file is not dictated by the specifications. If you want to rely on it, you have to either (1) know for a fact that your specific implementation uses the same order as the definition order (testing it, like you've done, is a good idea but does not guarantee anything), or (2) change the order yourself.