Package proguard.classfile.visitor

This package contains interfaces and classes for processing class files from the proguard.classfile package using the visitor pattern.

See:
Description

Interface Summary

ClassPoolVisitor	This interface specifies the methods for a visitor of ClassPool objects.
ClassVisitor	This interface specifies the methods for a visitor of Clazz objects.
MemberVisitor	This interface specifies the methods for a visitor of ProgramMember objects and LibraryMember objects.

Class Summary

AllClassVisitor	This ClassPoolVisitor lets a given ClassVisitor visit all Clazz objects of the class pools it visits.
AllFieldVisitor	This ClassVisitor lets a given MemberVisitor visit all FieldMember objects of the classes it visits.
AllMemberVisitor	This ClassVisitor lets a given MemberVisitor visit all Member objects of the classes it visits.
AllMethodVisitor	This ClassVisitor lets a given MemberVisitor visit all MethodMember objects of the classes it visits.
BottomClassFilter	This ClassVisitor delegates its visits to another given ClassVisitor, but only when visiting classes that don't have any subclasses.
ClassAccessFilter	This ClassVisitor delegates its visits to another given ClassVisitor, but only when the visited class has the proper access flags.
ClassCleaner	This ClassVisitor removes all visitor information of the classes it visits.
ClassCollector	This ClassVisitor collects the classes that it visits in the given collection.
ClassCounter	This ClassVisitor counts the number of classes that has been visited.
ClassForNameClassVisitor	This ConstantVisitor lets a given ClassVisitor visit all constant classes involved in any Class.forName constructs that it visits.
ClassHierarchyTraveler	This ClassVisitor lets a given ClassVisitor optionally travel to the visited class, its superclass, its interfaces, and its subclasses.
ClassNameFilter	This ClassVisitor delegates its visits to another given ClassVisitor, but only when the visited class has a name that matches a given regular expression.
ClassPoolFiller	This ClassVisitor collects all the classes it visits in a given class pool.
ClassPresenceFilter	This ClassVisitor delegates its visits to one of two ClassVisitor instances, depending on whether the name of the visited class file is present in a given ClassPool or not.
ClassPrinter	This ClassVisitor prints out the complete internal structure of the classes it visits.
ClassVersionFilter	This ClassVisitor delegates its visits to program classes to another given ClassVisitor, but only when the class version number of the visited program class lies in a given range.
ClassVersionSetter	This ClassVisitor sets the version number of the program classes that it visits.
ConcreteClassDownTraveler	This ClassVisitor lets a given ClassVisitor travel to the first concrete subclasses down in its hierarchy of abstract classes and concrete classes.
DotClassClassVisitor	This InstructionVisitor lets a given ClassVisitor visit all classes involved in any .class constructs that it visits.
ExceptClassesFilter	This ClassVisitor delegates its visits to another given ClassVisitor, except for classes are in a given list.
ExceptClassFilter	This ClassVisitor delegates its visits to another given ClassVisitor, except for one given class.
ExceptionCounter	This ExceptionInfoVisitor counts the number of exceptions that has been visited.
ExceptionExcludedOffsetFilter	This ExceptionInfoVisitor delegates its visits to another given ExceptionInfoVisitor, but only when the visited exception does not cover the instruction at the given offset.
ExceptionHandlerConstantVisitor	This ExceptionInfoVisitor lets a given ConstantVisitor visit all catch class constants of exceptions that it visits.
ExceptionHandlerFilter	This ExceptionInfoVisitor delegates its visits to another given ExceptionInfoVisitor, but only when the visited exception targets an instruction in the given range of offsets.
ExceptionOffsetFilter	This ExceptionInfoVisitor delegates its visits to another given ExceptionInfoVisitor, but only when the visited exception covers the instruction at the given offset.
ExceptionRangeFilter	This ExceptionInfoVisitor delegates its visits to another given ExceptionInfoVisitor, but only when the visited exception overlaps with the given instruction range.
ImplementedClassConstantFilter	This ConstantVisitor delegates its visits to class constants to another given ConstantVisitor, except for classes that extend or implement a given class.
ImplementedClassFilter	This ClassVisitor delegates its visits to another given ClassVisitor, except for classes that extend or implement a given class.
ImplementingClassConstantFilter	This ConstantVisitor delegates its visits to class constants to another given ConstantVisitor, except for classes that are extended or implemented by a given class.
LibraryClassFilter	This ClassVisitor delegates its visits to another given ClassVisitor, but only when visiting library classes.
LibraryMemberFilter	This MemberVisitor delegates its visits to another given MemberVisitor, but only when visiting members of library classes.
MemberAccessFilter	This MemberVisitor delegates its visits to another given MemberVisitor, but only when the visited member has the proper access flags.
MemberClassAccessFilter	This MemberVisitor delegates its visits to another given MemberVisitor, but only when the visited member is accessible from the given referencing class.
MemberCollector	This MemberVisitor collects the concatenated name/descriptor strings of class members that have been visited.
MemberCounter	This MemberVisitor counts the number of class members that have been visited.
MemberDescriptorFilter	This MemberVisitor delegates its visits to another given MemberVisitor, but only when the visited member has a descriptor that matches a given regular expression.
MemberNameFilter	This MemberVisitor delegates its visits to another given MemberVisitor, but only when the visited member has a name that matches a given regular expression.
MemberToClassVisitor	This MemberVisitor delegates all visits to a given ClassVisitor.
MethodImplementationFilter	This MemberVisitor delegates its visits to methods to another given MemberVisitor, but only when the visited method may have implementations.
MethodImplementationTraveler	This MemberVisitor lets a given MemberVisitor travel to all concrete and abstract implementations of the visited methods in their class hierarchies.
MultiClassPoolVisitor	This ClassPoolVisitor delegates all visits to each ClassPoolVisitor in a given list.
MultiClassVisitor	This ClassVisitor delegates all visits to each ClassVisitor in a given list.
MultiMemberVisitor	This MemberVisitor delegates all visits to each MemberVisitor in a given list.
NamedClassVisitor	This class visits Clazz objects with the given name.
NamedFieldVisitor	This class visits ProgramMember objects referring to fields, identified by a name and descriptor pair.
NamedMethodVisitor	This class visits ProgramMember objects referring to methods, identified by a name and descriptor pair.
ProgramClassFilter	This ClassVisitor delegates its visits to another given ClassVisitor, but only when visiting program classes.
ProgramMemberFilter	This MemberVisitor delegates its visits to another given MemberVisitor, but only when visiting members of program classes.
ReferencedClassVisitor	This ClassVisitor, MemberVisitor, ConstantVisitor, AttributeVisitor, etc.
ReferencedMemberVisitor	This ConstantVisitor and ElementValueVisitor lets a given MemberVisitor visit all the referenced class members of the elements that it visits.
SimilarMemberVisitor	This MemberVisitor lets a given MemberVisitor visit all members that have the same name and type as the visited methods in the class hierarchy of a given target class.
SimpleClassPrinter	This ClassVisitor and MemberVisitor prints out the class names of the classes it visits, and the full class member descriptions of the class members it visits.
SubclassFilter	This ClassVisitor delegates its visits to another given ClassVisitor, except for classes that have a given class as direct subclass.
SubclassTraveler	This ClassVisitor lets a given ClassVisitor travel to direct subclasses of the visited class.
VariableClassVisitor	This ClassVisitor delegates all method calls to a ClassVisitor that can be changed at any time.
VariableMemberVisitor	This MemberVisitor delegates all method calls to a MemberVisitor that can be changed at any time.

Package proguard.classfile.visitor Description

This package contains interfaces and classes for processing class files from the proguard.classfile package using the visitor pattern. Cfr., for instance, "Design Patterns, Elements of Reusable OO Software", by Gamma, Helm, Johnson, and Vlissider.

Why the visitor pattern? Class files frequently contain lists of elements of various mixed types: class items, constant pool entries, attributes,... These lists and types are largely fixed; they won't change much in future releases of the Java class file specifications. On the other hand, the kinds of operations that we may wish to perform on the class files may change and expand. We want to separate the objects and the operations performed upon them. This is a good place to use the visitor pattern.

Visitor interfaces avoid having to do series of instanceof tests on the elements of a list, followed by type casts and the proper operations. Every list element is a visitor accepter. When its accept method is called by a visitor, it calls its corresponding visitX method in the visitor, passing itself as an argument. This technique is called double-dispatch.

As already mentioned, the main advantage is avoiding lots of instanceof tests and type casts. Also, implementing a visitor interface ensures you're handling all possible visitor accepter types. Each type has its own method, which you simply have to implement.

A disadvantage is that the visitor methods always get the same names, specified by the visitor interface. These names aren't descriptive at all, making code harder to read. It's the visitor classes that describe the operations now.

Also, the visitor methods always have the same parameters and return values, as specified by the visitor interfaces. Passing additional parameters is done by means of extra fields in the visitor, which is somewhat of a kludge.

Because objects (the visitor accepters) and the operations performed upon them (the visitors) are now separated, it becomes harder to associate some state with the objects. For convenience, we always provide an extra visitor info field in visitor accepters, in which visitors can put any temporary information they want.