org.objectweb.asm
Class ClassWriter

java.lang.Object
  extended by org.objectweb.asm.ClassWriter
All Implemented Interfaces:
ClassVisitor

public class ClassWriter
extends Object
implements ClassVisitor

A ClassVisitor that generates classes in bytecode form. More precisely this visitor generates a byte array conforming to the Java class file format. It can be used alone, to generate a Java class "from scratch", or with one or more ClassReader and adapter class visitor to generate a modified class from one or more existing Java classes.

Author:
Eric Bruneton

Field Summary
static int COMPUTE_FRAMES
          Flag to automatically compute the stack map frames of methods from scratch.
static int COMPUTE_MAXS
          Flag to automatically compute the maximum stack size and the maximum number of local variables of methods.
 
Constructor Summary
ClassWriter(ClassReader classReader, int flags)
          Constructs a new ClassWriter object and enables optimizations for "mostly add" bytecode transformations.
ClassWriter(int flags)
          Constructs a new ClassWriter object.
 
Method Summary
protected  String getCommonSuperClass(String type1, String type2)
          Returns the common super type of the two given types.
 int newClass(String value)
          Adds a class reference to the constant pool of the class being build.
 int newConst(Object cst)
          Adds a number or string constant to the constant pool of the class being build.
 int newField(String owner, String name, String desc)
          Adds a field reference to the constant pool of the class being build.
 int newMethod(String owner, String name, String desc, boolean itf)
          Adds a method reference to the constant pool of the class being build.
 int newNameType(String name, String desc)
          Adds a name and type to the constant pool of the class being build.
 int newUTF8(String value)
          Adds an UTF8 string to the constant pool of the class being build.
 byte[] toByteArray()
          Returns the bytecode of the class that was build with this class writer.
 void visit(int version, int access, String name, String signature, String superName, String[] interfaces)
          Visits the header of the class.
 AnnotationVisitor visitAnnotation(String desc, boolean visible)
          Visits an annotation of the class.
 void visitAttribute(Attribute attr)
          Visits a non standard attribute of the class.
 void visitEnd()
          Visits the end of the class.
 FieldVisitor visitField(int access, String name, String desc, String signature, Object value)
          Visits a field of the class.
 void visitInnerClass(String name, String outerName, String innerName, int access)
          Visits information about an inner class.
 MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions)
          Visits a method of the class.
 void visitOuterClass(String owner, String name, String desc)
          Visits the enclosing class of the class.
 void visitSource(String file, String debug)
          Visits the source of the class.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

COMPUTE_MAXS

public static final int COMPUTE_MAXS
Flag to automatically compute the maximum stack size and the maximum number of local variables of methods. If this flag is set, then the arguments of the visitMaxs method of the MethodVisitor returned by the visitMethod method will be ignored, and computed automatically from the signature and the bytecode of each method.

See Also:
ClassWriter(int), Constant Field Values

COMPUTE_FRAMES

public static final int COMPUTE_FRAMES
Flag to automatically compute the stack map frames of methods from scratch. If this flag is set, then the calls to the MethodVisitor.visitFrame(int, int, java.lang.Object[], int, java.lang.Object[]) method are ignored, and the stack map frames are recomputed from the methods bytecode. The arguments of the visitMaxs method are also ignored and recomputed from the bytecode. In other words, computeFrames implies computeMaxs.

See Also:
ClassWriter(int), Constant Field Values
Constructor Detail

ClassWriter

public ClassWriter(int flags)
Constructs a new ClassWriter object.

Parameters:
flags - option flags that can be used to modify the default behavior of this class. See COMPUTE_MAXS, COMPUTE_FRAMES.

ClassWriter

public ClassWriter(ClassReader classReader,
                   int flags)
Constructs a new ClassWriter object and enables optimizations for "mostly add" bytecode transformations. These optimizations are the following:

Parameters:
classReader - the ClassReader used to read the original class. It will be used to copy the entire constant pool from the original class and also to copy other fragments of original bytecode where applicable.
flags - option flags that can be used to modify the default behavior of this class. See COMPUTE_MAXS, COMPUTE_FRAMES.
Method Detail

visit

public void visit(int version,
                  int access,
                  String name,
                  String signature,
                  String superName,
                  String[] interfaces)
Description copied from interface: ClassVisitor
Visits the header of the class.

Specified by:
visit in interface ClassVisitor
Parameters:
version - the class version.
access - the class's access flags (see Opcodes). This parameter also indicates if the class is deprecated.
name - the internal name of the class (see getInternalName).
signature - the signature of this class. May be null if the class is not a generic one, and does not extend or implement generic classes or interfaces.
superName - the internal of name of the super class (see getInternalName). For interfaces, the super class is Object. May be null, but only for the Object class.
interfaces - the internal names of the class's interfaces (see getInternalName). May be null.

visitSource

public void visitSource(String file,
                        String debug)
Description copied from interface: ClassVisitor
Visits the source of the class.

Specified by:
visitSource in interface ClassVisitor
Parameters:
file - the name of the source file from which the class was compiled. May be null.
debug - additional debug information to compute the correspondance between source and compiled elements of the class. May be null.

visitOuterClass

public void visitOuterClass(String owner,
                            String name,
                            String desc)
Description copied from interface: ClassVisitor
Visits the enclosing class of the class. This method must be called only if the class has an enclosing class.

Specified by:
visitOuterClass in interface ClassVisitor
Parameters:
owner - internal name of the enclosing class of the class.
name - the name of the method that contains the class, or null if the class is not enclosed in a method of its enclosing class.
desc - the descriptor of the method that contains the class, or null if the class is not enclosed in a method of its enclosing class.

visitAnnotation

public AnnotationVisitor visitAnnotation(String desc,
                                         boolean visible)
Description copied from interface: ClassVisitor
Visits an annotation of the class.

Specified by:
visitAnnotation in interface ClassVisitor
Parameters:
desc - the class descriptor of the annotation class.
visible - true if the annotation is visible at runtime.
Returns:
a visitor to visit the annotation values, or null if this visitor is not interested in visiting this annotation.

visitAttribute

public void visitAttribute(Attribute attr)
Description copied from interface: ClassVisitor
Visits a non standard attribute of the class.

Specified by:
visitAttribute in interface ClassVisitor
Parameters:
attr - an attribute.

visitInnerClass

public void visitInnerClass(String name,
                            String outerName,
                            String innerName,
                            int access)
Description copied from interface: ClassVisitor
Visits information about an inner class. This inner class is not necessarily a member of the class being visited.

Specified by:
visitInnerClass in interface ClassVisitor
Parameters:
name - the internal name of an inner class (see getInternalName).
outerName - the internal name of the class to which the inner class belongs (see getInternalName). May be null for not member classes.
innerName - the (simple) name of the inner class inside its enclosing class. May be null for anonymous inner classes.
access - the access flags of the inner class as originally declared in the enclosing class.

visitField

public FieldVisitor visitField(int access,
                               String name,
                               String desc,
                               String signature,
                               Object value)
Description copied from interface: ClassVisitor
Visits a field of the class.

Specified by:
visitField in interface ClassVisitor
Parameters:
access - the field's access flags (see Opcodes). This parameter also indicates if the field is synthetic and/or deprecated.
name - the field's name.
desc - the field's descriptor (see Type).
signature - the field's signature. May be null if the field's type does not use generic types.
value - the field's initial value. This parameter, which may be null if the field does not have an initial value, must be an Integer, a Float, a Long, a Double or a String (for int, float, long or String fields respectively). This parameter is only used for static fields. Its value is ignored for non static fields, which must be initialized through bytecode instructions in constructors or methods.
Returns:
a visitor to visit field annotations and attributes, or null if this class visitor is not interested in visiting these annotations and attributes.

visitMethod

public MethodVisitor visitMethod(int access,
                                 String name,
                                 String desc,
                                 String signature,
                                 String[] exceptions)
Description copied from interface: ClassVisitor
Visits a method of the class. This method must return a new MethodVisitor instance (or null) each time it is called, i.e., it should not return a previously returned visitor.

Specified by:
visitMethod in interface ClassVisitor
Parameters:
access - the method's access flags (see Opcodes). This parameter also indicates if the method is synthetic and/or deprecated.
name - the method's name.
desc - the method's descriptor (see Type).
signature - the method's signature. May be null if the method parameters, return type and exceptions do not use generic types.
exceptions - the internal names of the method's exception classes (see getInternalName). May be null.
Returns:
an object to visit the byte code of the method, or null if this class visitor is not interested in visiting the code of this method.

visitEnd

public void visitEnd()
Description copied from interface: ClassVisitor
Visits the end of the class. This method, which is the last one to be called, is used to inform the visitor that all the fields and methods of the class have been visited.

Specified by:
visitEnd in interface ClassVisitor

toByteArray

public byte[] toByteArray()
Returns the bytecode of the class that was build with this class writer.

Returns:
the bytecode of the class that was build with this class writer.

newConst

public int newConst(Object cst)
Adds a number or string constant to the constant pool of the class being build. Does nothing if the constant pool already contains a similar item. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:
cst - the value of the constant to be added to the constant pool. This parameter must be an Integer, a Float, a Long, a Double or a String.
Returns:
the index of a new or already existing constant item with the given value.

newUTF8

public int newUTF8(String value)
Adds an UTF8 string to the constant pool of the class being build. Does nothing if the constant pool already contains a similar item. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:
value - the String value.
Returns:
the index of a new or already existing UTF8 item.

newClass

public int newClass(String value)
Adds a class reference to the constant pool of the class being build. Does nothing if the constant pool already contains a similar item. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:
value - the internal name of the class.
Returns:
the index of a new or already existing class reference item.

newField

public int newField(String owner,
                    String name,
                    String desc)
Adds a field reference to the constant pool of the class being build. Does nothing if the constant pool already contains a similar item. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:
owner - the internal name of the field's owner class.
name - the field's name.
desc - the field's descriptor.
Returns:
the index of a new or already existing field reference item.

newMethod

public int newMethod(String owner,
                     String name,
                     String desc,
                     boolean itf)
Adds a method reference to the constant pool of the class being build. Does nothing if the constant pool already contains a similar item. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:
owner - the internal name of the method's owner class.
name - the method's name.
desc - the method's descriptor.
itf - true if owner is an interface.
Returns:
the index of a new or already existing method reference item.

newNameType

public int newNameType(String name,
                       String desc)
Adds a name and type to the constant pool of the class being build. Does nothing if the constant pool already contains a similar item. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Parameters:
name - a name.
desc - a type descriptor.
Returns:
the index of a new or already existing name and type item.

getCommonSuperClass

protected String getCommonSuperClass(String type1,
                                     String type2)
Returns the common super type of the two given types. The default implementation of this method loads the two given classes and uses the java.lang.Class methods to find the common super class. It can be overridden to compute this common super type in other ways, in particular without actually loading any class, or to take into account the class that is currently being generated by this ClassWriter, which can of course not be loaded since it is under construction.

Parameters:
type1 - the internal name of a class.
type2 - the internal name of another class.
Returns:
the internal name of the common super class of the two given classes.