JVM, Class Files, and the CLEmitter - Introduction to Compiler Construction in a Java World - page 326

publicvoidaddMethod(ArrayList<String>accessFlags,
Stringname,
Stringdescriptor,
ArrayList<String>exceptions,
booleanisSynthetic)
where accessFlags is a list of method access and property flags, name is the name 9 of the
method, descriptor is the method descriptor, exceptions is a list of exceptions in internal
form that this method throws, and isSythetic specifies whether the method is created by
the compiler.
For example, one may add a method using
accessFlags.add("public");
output.addMethod(accessFlags,"factorial","(I)I",exceptions,false);
where accessFlags is a list of method access and property ags, \factorial" is the name 10
of the method, \(I)I" is the method descriptor, exceptions is a list of exceptions in internal
form that this method throws, and the argument false indicates that the method appears
in source code.
A comment on the method descriptor is warranted. The method descriptor describes the
method's signature in a format internal to the JVM. The I is the internal type descriptor for
the primitive type . , so the \(I)I" species that the method takes one integer argument
and returns a value having integer type.
Add Exception Handlers to Method
An exception handler to code a try-catch block can be added to a method by sending to
the CLEmitter instance the following message:
publicvoidaddExceptionHandler(StringstartLabel,
StringendLabel,
StringhandlerLabel,
StringcatchType)
where startLabel marks the beginning of the try block, endLabel marks the end of the
try block, handlerLabel marks the beginning of a catch block, and catchType specifies
the exception that is to be caught in internal form. If catchType is null , this exception
handler is called for all exceptions; this is used to implement finally .
createLabel() and addLabel(Stringlabel) can be invoked on the CLEmitter in-
stance to create unique labels and for adding them to mark instructions in the code indi-
cating where to jump to.
A method can specify as many exception handlers as there are exceptions that are being
caught in the method.
Add Optional Method, Field, Class, Code Attributes
Attributes are used in the ClassFile ( CLFile ), field_info (CLFieldInfo), method_info
( CLMethodInfo ), and Code_attribute ( CLCodeAttribute ) structures of the class file
format. While there are many kinds of attributes, only some are mandatory; these
include InnerClasses_attribute (class attribute), Synthetic_attribute (class, field,
and method attribute), Code_attribute (method attribute), and Exceptions_attribute
(method attribute).
CLEmitter implicitly adds the required attributes to the appropriate structures. The
9 Instance initializers must have the name <init> and static initializers must have the name <clinit> .
10 Instance constructors must have the name <init> .