java asm methodvisitor 定义局部变量,ASM字节码工程库中MethodVisitor类的visitLocalVariable()方法有什么作用?...

I am using ASM (for the first time) in an application to create Java class files. This is for the backend of a compiler I am writing.

I read the relevant parts of the ASM documentation and have a question about stack map frames. ASM says it can automatically compute those frames if the class writer is initialized with the appropriate flags. My question is, does that mean I will not ever have to call the visitLocalVariable() method on the method visitors myself? I am not sure what that method does. The documentation does say that I do not need to call the visitFrame() method if frames are computed automatically, but it is silent on the visitLocalVariable() method.

解决方案

visitLocalVariable() describes or defines the debug information as stored in the LocalVariableTable and LocalVariableTypeTable attributes of a Code attribute. They are not required for normal operation and distinct from the information stored in a StackMapTable.

In other words, unless you want to provide debug information, you never need to call visitLocalVariable(), regardless of whether stack map frames are automatically computed or not.

Note the differences of the information stored within these attributes. LocalVariable[Type]Table stores names and [generic] types of local variables and their scope regarding the source level language. StackMapTable stores type information for local variables and operand stack entries regarding the JVM type system for the byte code verifier.