JVM, Class Files, and the CLEmitter - Introduction to Compiler Construction in a Java World - page 322

MethodDescriptor ::= ( fParameterDescriptorg ) ReturnDescriptor

ParameterDescriptor ::= FieldType

ReturnDescriptor ::= FieldType j V

For example, the table below indicates the method descriptors for various constructor
and method declarations:

Constructor/Method Descriptor

publicQueue() ()V
publicFile[]listFiles() ()[Ljava/io/File;
publicBooleanisPrime(intn) (I)Ljava/lang/Boolean;
publicstaticvoidmain(String[]args)([L/java/lang/String;)V

D.4 CLEmitter
D.4.1 CLEmitter Operation
The j-- compiler's purpose is to produce a class le. Given the complexity of class les we
supply a tool called the CLEmitter to ease the generation of code and the creation of class
files. The CLEmitter 6 has a relatively small set of methods that support

The creation of a class or an interface;

The addition of fields and methods to the class;

The addition of instructions, exception handlers, and code attributes to methods;

The addition of inner classes;

Optional field, method, and class attributes;

Checking for errors; and

The writing of the class file to the file system.

While it is much simpler to work with an interface like CLEmitter , one still must be
aware of certain aspects of the target machine, such as the instruction set.
Figure D.3 outlines the necessary steps for creating an in-memory representation of a
class file using the CLEmitter interface, and then writing that class file to the file system.

6 This is a class in the jminusminus package under $j/j--/src folder. The classes that CLEmitter
depends on are also in that package and have a CL prex.