Package net.sf.jode.bytecode

Provides easy access to class files and their contents.

See:
Description

Interface Summary

Opcodes

This is an interface containing the constants for the byte code opcodes.

Class Summary

BasicBlocks	Represents the byte code of a method in form of basic blocks.
BinaryInfo	Represents a container for user specified attributes.
Block	Represents a single basic block.
ClassInfo	Represents a class or interface.
ClassPath	A path in which class files are searched for.
ClassPath.Location	A location is a single component of the ClassPath.
ConstantPool	This class represent the constant pool.
FieldInfo	Represents a java bytecode field (class variable).
GrowableConstantPool	This class represent a constant pool, where new constants can be added to.
Handler	A simple class containing the info about one try-catch block.
Instruction	This class represents an instruction in the byte code.
LocalVariableInfo	A simple class containing the info of the LocalVariableTable.
MethodInfo	Represents a java bytecode method.
Reference	This class represents a field or method reference.
TypeSignature	This class contains some static methods to handle type signatures.

Exception Summary

ClassFormatException

Thrown when a class file with an unknown or illegal format is loaded.

Package net.sf.jode.bytecode Description

Provides easy access to class files and their contents. To use it you create a ClassPath object giving it the locations where it should search for classes. Then you can ask this object for a class and get a ClassInfo object. As third step you can actually load the class.

Please notify me if you want to use this package. I will inform you about updates, help you with problems, etc. WARNING: Some parts of this package may change in the future in incompatible ways. Ask me for more information.

Here is a short example, how you can use this package, see the documentation of the classes for more details.

 ...
 ClassPath path = new ClassPath("/usr/lib/java/lib/classes.zip");
 ClassInfo clazz = path.getClassInfo("java.util.Hashtable");

 try {
   clazz.load(ClassInfo.DECLARATIONS);
 } catch (ClassFormatException ex) {
   System.err.println("Something is wrong with HashTable, giving up!");
   return;
 } catch (IOException ex) {
   System.err.println("Can't load HashTable, giving up!");
   return;
 }

 MethodInfo[] methods = clazz.getMethods();
 for (int i = 0; i < methods.length; i++) {
     String type = methods[i].getType();
     if (TypeSignature.getReturnType(type) == TypeSignature.INT_TYPE)
         System.out.println("Found integer method: "+method.getName());
 }
 ...

You can also use this package to create and write new classes:

 ...
 ClassPath path = new ClassPath("/usr/lib/java/lib/classes.zip");
 ClassInfo clazz = path.getClassInfo("my.new.Class");
 clazz.setModifiers(Modifier.PUBLIC);
 clazz.setSourceFile("Class.pl");
 clazz.set...
 clazz.write(zipOutputStream);
 ...

Advantages of this bytecode package

• You don't need to think of the constant pool, except when you want to write your custom attributes.
• The set of opcodes is drastically reduced: For example you don't have to handle 20 different opcodes that all push a constant value on the stack. When reading it will automatically convert them to ldc or ldc2 and on writing it will convert them back.
• Wide instructions are automatically generated when needed, large methods are supported.
• The code is organized in BasicBlocks which makes flow analysis much easier.
• The memory consumption is quite moderate.

Disadvantages

• You can't change every byte. For example Jode decides itself if a lookup switch or table switch is generated.
• Jode does a lot of checks when reading the bytecode and it is impossible to recover from errors. This makes it sometime hard to find out why the bytecode of a particular class files is invalid.

Jochen Hoenicke

Last modified: Sat Aug 11 18:44:19 MEST 2001