Java Bytecode Signatures

As part of the compiler for the programming language I am working on, I came across generic signatures in the bytecode, which I am trying to parse and convert to an AST. The parsing algorithm mostly works, but there seems to be a special case in which the format of these signatures behaves a bit strangely. Here are a few of these cases:

java.util.Arrays#parallelSort: <T::Ljava/lang/Comparable<-TT;>;>([TT;)V
java.util.Arrays#parallelSort: <T::Ljava/lang/Comparable<-TT;>;>([TT;II)V
java.lang.Class#getAnnotation: <A::Ljava/lang/annotation/Annotation;>(Ljava/lang/Class<TA;>;)TA;
java.lang.Class#getAnnotationsByType: <A::Ljava/lang/annotation/Annotation;>(Ljava/lang/Class<TA;>;)[TA;
java.lang.Class#getDeclaredAnnotation: <A::Ljava/lang/annotation/Annotation;>(Ljava/lang/Class<TA;>;)TA;
java.lang.Class#getDeclaredAnnotationsByType: <A::Ljava/lang/annotation/Annotation;>(Ljava/lang/Class<TA;>;)[TA;
java.util.Arrays#parallelSort: <T::Ljava/lang/Comparable<-TT;>;>([TT;)V
java.util.Arrays#parallelSort: <T::Ljava/lang/Comparable<-TT;>;>([TT;II)V
java.util.Collections#sort: <T::Ljava/lang/Comparable<-TT;>;>(Ljava/util/List<TT;>;)V

Out of all the methods in these classes, these are the only ones that have :: in their signature. My question is what this token does and why it exists.


I know about the :: operator in the Java Language, but this is something on the Bytecode level.


There is a defined syntax that changed as of JSR 14 to specify the bounds of a generic type.


So for your example of:


Which would reflect:

<T extends Comparable<T>>

The variable name is T, there is no class type bound so it was omitted, and there was an interface bound of type Comparable<T>.

All your example follow this, but there any many different forms:



Leave a Reply

Your email address will not be published. Required fields are marked *