Package org.springframework.asm
Class ClassWriter
java.lang.Object
org.springframework.asm.ClassVisitor
org.springframework.asm.ClassWriter
A
ClassVisitor
that generates a corresponding ClassFile structure, as defined in the Java
Virtual Machine Specification (JVMS). It can be used alone, to generate a Java class "from
scratch", or with one or more ClassReader
and adapter ClassVisitor
to generate a
modified class from one or more existing Java classes.- Author:
- Eric Bruneton
- See Also:
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Field Summary
Modifier and TypeFieldDescriptionstatic final int
A flag to automatically compute the stack map frames of methods from scratch.static final int
A flag to automatically compute the maximum stack size and the maximum number of local variables of methods.Fields inherited from class org.springframework.asm.ClassVisitor
api, cv
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Constructor Summary
ConstructorDescriptionClassWriter
(int flags) Constructs a newClassWriter
object.ClassWriter
(ClassReader classReader, int flags) Constructs a newClassWriter
object and enables optimizations for "mostly add" bytecode transformations. -
Method Summary
Modifier and TypeMethodDescriptionprotected ClassLoader
Returns theClassLoader
to be used by the default implementation ofgetCommonSuperClass(String, String)
, that of thisClassWriter
's runtime type by default.protected String
getCommonSuperClass
(String type1, String type2) Returns the common super type of the two given types.boolean
hasFlags
(int flags) Returns true if all the given flags were passed to the constructor.int
Adds a class reference to the constant pool of the class being build.int
Adds a number or string constant to the constant pool of the class being build.int
newConstantDynamic
(String name, String descriptor, Handle bootstrapMethodHandle, Object... bootstrapMethodArguments) Adds a dynamic constant reference to the constant pool of the class being build.int
Adds a field reference to the constant pool of the class being build.int
Deprecated.int
Adds a handle to the constant pool of the class being build.int
newInvokeDynamic
(String name, String descriptor, Handle bootstrapMethodHandle, Object... bootstrapMethodArguments) Adds an invokedynamic reference to the constant pool of the class being build.int
Adds a method reference to the constant pool of the class being build.int
newMethodType
(String methodDescriptor) Adds a method type reference to the constant pool of the class being build.int
Adds a module reference to the constant pool of the class being build.int
newNameType
(String name, String descriptor) Adds a name and type to the constant pool of the class being build.int
newPackage
(String packageName) Adds a package reference to the constant pool of the class being build.int
Adds an UTF8 string to the constant pool of the class being build.byte[]
Returns the content of the class file that was built by this ClassWriter.final void
visit
(int version, int access, String name, String signature, String superName, String[] interfaces) Visits the header of the class.final AnnotationVisitor
visitAnnotation
(String descriptor, boolean visible) Visits an annotation of the class.final void
visitAttribute
(Attribute attribute) Visits a non standard attribute of the class.final void
visitEnd()
Visits the end of the class.final FieldVisitor
visitField
(int access, String name, String descriptor, String signature, Object value) Visits a field of the class.final void
visitInnerClass
(String name, String outerName, String innerName, int access) Visits information about an inner class.final MethodVisitor
visitMethod
(int access, String name, String descriptor, String signature, String[] exceptions) Visits a method of the class.final ModuleVisitor
visitModule
(String name, int access, String version) Visit the module corresponding to the class.final void
visitNestHost
(String nestHost) Visits the nest host class of the class.final void
visitNestMember
(String nestMember) Visits a member of the nest.final void
visitOuterClass
(String owner, String name, String descriptor) Visits the enclosing class of the class.final void
visitPermittedSubclass
(String permittedSubclass) Visits a permitted subclasses.final RecordComponentVisitor
visitRecordComponent
(String name, String descriptor, String signature) Visits a record component of the class.final void
visitSource
(String file, String debug) Visits the source of the class.final AnnotationVisitor
visitTypeAnnotation
(int typeRef, TypePath typePath, String descriptor, boolean visible) Visits an annotation on a type in the class signature.Methods inherited from class org.springframework.asm.ClassVisitor
getDelegate
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Field Details
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COMPUTE_MAXS
public static final int COMPUTE_MAXSA 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 theMethodVisitor.visitMaxs(int, int)
method of theMethodVisitor
returned by thevisitMethod(int, java.lang.String, java.lang.String, java.lang.String, java.lang.String[])
method will be ignored, and computed automatically from the signature and the bytecode of each method.Note: for classes whose version is
Opcodes.V1_7
of more, this option requires valid stack map frames. The maximum stack size is then computed from these frames, and from the bytecode instructions in between. If stack map frames are not present or must be recomputed, usedCOMPUTE_FRAMES
instead.- See Also:
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COMPUTE_FRAMES
public static final int COMPUTE_FRAMESA flag to automatically compute the stack map frames of methods from scratch. If this flag is set, then the calls to theMethodVisitor.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 theMethodVisitor.visitMaxs(int, int)
method are also ignored and recomputed from the bytecode. In other words,COMPUTE_FRAMES
impliesCOMPUTE_MAXS
.- See Also:
-
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Constructor Details
-
ClassWriter
public ClassWriter(int flags) Constructs a newClassWriter
object.- Parameters:
flags
- option flags that can be used to modify the default behavior of this class. Must be zero or more ofCOMPUTE_MAXS
andCOMPUTE_FRAMES
.
-
ClassWriter
Constructs a newClassWriter
object and enables optimizations for "mostly add" bytecode transformations. These optimizations are the following:- The constant pool and bootstrap methods from the original class are copied as is in the new class, which saves time. New constant pool entries and new bootstrap methods will be added at the end if necessary, but unused constant pool entries or bootstrap methods won't be removed.
- Methods that are not transformed are copied as is in the new class, directly from the
original class bytecode (i.e. without emitting visit events for all the method
instructions), which saves a lot of time. Untransformed methods are detected by
the fact that the
ClassReader
receivesMethodVisitor
objects that come from aClassWriter
(and not from any otherClassVisitor
instance).
- Parameters:
classReader
- theClassReader
used to read the original class. It will be used to copy the entire constant pool and bootstrap methods 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. Must be zero or more ofCOMPUTE_MAXS
andCOMPUTE_FRAMES
. These option flags do not affect methods that are copied as is in the new class. This means that neither the maximum stack size nor the stack frames will be computed for these methods.
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Method Details
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hasFlags
public boolean hasFlags(int flags) Returns true if all the given flags were passed to the constructor.- Parameters:
flags
- some option flags. Must be zero or more ofCOMPUTE_MAXS
andCOMPUTE_FRAMES
.- Returns:
- true if all the given flags, or more, were passed to the constructor.
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visit
public final void visit(int version, int access, String name, String signature, String superName, String[] interfaces) Description copied from class:ClassVisitor
Visits the header of the class.- Overrides:
visit
in classClassVisitor
- Parameters:
version
- the class version. The minor version is stored in the 16 most significant bits, and the major version in the 16 least significant bits.access
- the class's access flags (seeOpcodes
). This parameter also indicates if the class is deprecatedOpcodes.ACC_DEPRECATED
or a recordOpcodes.ACC_RECORD
.name
- the internal name of the class (seeType.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 (seeType.getInternalName()
). For interfaces, the super class isObject
. May be null, but only for theObject
class.interfaces
- the internal names of the class's interfaces (seeType.getInternalName()
). May be null.
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visitSource
Description copied from class:ClassVisitor
Visits the source of the class.- Overrides:
visitSource
in classClassVisitor
- Parameters:
file
- the name of the source file from which the class was compiled. May be null.debug
- additional debug information to compute the correspondence between source and compiled elements of the class. May be null.
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visitModule
Description copied from class:ClassVisitor
Visit the module corresponding to the class.- Overrides:
visitModule
in classClassVisitor
- Parameters:
name
- the fully qualified name (using dots) of the module.access
- the module access flags, amongACC_OPEN
,ACC_SYNTHETIC
andACC_MANDATED
.version
- the module version, or null.- Returns:
- a visitor to visit the module values, or null if this visitor is not interested in visiting this module.
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visitNestHost
Description copied from class:ClassVisitor
Visits the nest host class of the class. A nest is a set of classes of the same package that share access to their private members. One of these classes, called the host, lists the other members of the nest, which in turn should link to the host of their nest. This method must be called only once and only if the visited class is a non-host member of a nest. A class is implicitly its own nest, so it's invalid to call this method with the visited class name as argument.- Overrides:
visitNestHost
in classClassVisitor
- Parameters:
nestHost
- the internal name of the host class of the nest (seeType.getInternalName()
).
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visitOuterClass
Description copied from class:ClassVisitor
Visits the enclosing class of the class. This method must be called only if this class is a local or anonymous class. See the JVMS 4.7.7 section for more details.- Overrides:
visitOuterClass
in classClassVisitor
- Parameters:
owner
- internal name of the enclosing class of the class (seeType.getInternalName()
).name
- the name of the method that contains the class, or null if the class is not enclosed in a method or constructor of its enclosing class (e.g. if it is enclosed in an instance initializer, static initializer, instance variable initializer, or class variable initializer).descriptor
- the descriptor of the method that contains the class, or null if the class is not enclosed in a method or constructor of its enclosing class (e.g. if it is enclosed in an instance initializer, static initializer, instance variable initializer, or class variable initializer).
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visitAnnotation
Description copied from class:ClassVisitor
Visits an annotation of the class.- Overrides:
visitAnnotation
in classClassVisitor
- Parameters:
descriptor
- 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.
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visitTypeAnnotation
public final AnnotationVisitor visitTypeAnnotation(int typeRef, TypePath typePath, String descriptor, boolean visible) Description copied from class:ClassVisitor
Visits an annotation on a type in the class signature.- Overrides:
visitTypeAnnotation
in classClassVisitor
- Parameters:
typeRef
- a reference to the annotated type. The sort of this type reference must beTypeReference.CLASS_TYPE_PARAMETER
,TypeReference.CLASS_TYPE_PARAMETER_BOUND
orTypeReference.CLASS_EXTENDS
. SeeTypeReference
.typePath
- the path to the annotated type argument, wildcard bound, array element type, or static inner type within 'typeRef'. May be null if the annotation targets 'typeRef' as a whole.descriptor
- 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.
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visitAttribute
Description copied from class:ClassVisitor
Visits a non standard attribute of the class.- Overrides:
visitAttribute
in classClassVisitor
- Parameters:
attribute
- an attribute.
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visitNestMember
Description copied from class:ClassVisitor
Visits a member of the nest. A nest is a set of classes of the same package that share access to their private members. One of these classes, called the host, lists the other members of the nest, which in turn should link to the host of their nest. This method must be called only if the visited class is the host of a nest. A nest host is implicitly a member of its own nest, so it's invalid to call this method with the visited class name as argument.- Overrides:
visitNestMember
in classClassVisitor
- Parameters:
nestMember
- the internal name of a nest member (seeType.getInternalName()
).
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visitPermittedSubclass
Description copied from class:ClassVisitor
Visits a permitted subclasses. A permitted subclass is one of the allowed subclasses of the current class.- Overrides:
visitPermittedSubclass
in classClassVisitor
- Parameters:
permittedSubclass
- the internal name of a permitted subclass (seeType.getInternalName()
).
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visitInnerClass
Description copied from class:ClassVisitor
Visits information about an inner class. This inner class is not necessarily a member of the class being visited. More precisely, every class or interface C which is referenced by this class and which is not a package member must be visited with this method. This class must reference its nested class or interface members, and its enclosing class, if any. See the JVMS 4.7.6 section for more details.- Overrides:
visitInnerClass
in classClassVisitor
- Parameters:
name
- the internal name of C (seeType.getInternalName()
).outerName
- the internal name of the class or interface C is a member of (seeType.getInternalName()
). Must be null if C is not the member of a class or interface (e.g. for local or anonymous classes).innerName
- the (simple) name of C. Must be null for anonymous inner classes.access
- the access flags of C originally declared in the source code from which this class was compiled.
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visitRecordComponent
public final RecordComponentVisitor visitRecordComponent(String name, String descriptor, String signature) Description copied from class:ClassVisitor
Visits a record component of the class.- Overrides:
visitRecordComponent
in classClassVisitor
- Parameters:
name
- the record component name.descriptor
- the record component descriptor (seeType
).signature
- the record component signature. May be null if the record component type does not use generic types.- Returns:
- a visitor to visit this record component annotations and attributes, or null if this class visitor is not interested in visiting these annotations and attributes.
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visitField
public final FieldVisitor visitField(int access, String name, String descriptor, String signature, Object value) Description copied from class:ClassVisitor
Visits a field of the class.- Overrides:
visitField
in classClassVisitor
- Parameters:
access
- the field's access flags (seeOpcodes
). This parameter also indicates if the field is synthetic and/or deprecated.name
- the field's name.descriptor
- the field's descriptor (seeType
).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 anInteger
, aFloat
, aLong
, aDouble
or aString
(forint
,float
,long
orString
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.
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visitMethod
public final MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions) Description copied from class:ClassVisitor
Visits a method of the class. This method must return a newMethodVisitor
instance (or null) each time it is called, i.e., it should not return a previously returned visitor.- Overrides:
visitMethod
in classClassVisitor
- Parameters:
access
- the method's access flags (seeOpcodes
). This parameter also indicates if the method is synthetic and/or deprecated.name
- the method's name.descriptor
- the method's descriptor (seeType
).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 (seeType.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.
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visitEnd
public final void visitEnd()Description copied from class: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.- Overrides:
visitEnd
in classClassVisitor
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toByteArray
public byte[] toByteArray()Returns the content of the class file that was built by this ClassWriter.- Returns:
- the binary content of the JVMS ClassFile structure that was built by this ClassWriter.
- Throws:
ClassTooLargeException
- if the constant pool of the class is too large.MethodTooLargeException
- if the Code attribute of a method is too large.
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newConst
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 forAttribute
sub classes, and is normally not needed by class generators or adapters. -
newUTF8
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 forAttribute
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.
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newClass
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 forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
value
- the internal name of the class (seeType.getInternalName()
).- Returns:
- the index of a new or already existing class reference item.
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newMethodType
Adds a method type 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 forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
methodDescriptor
- method descriptor of the method type.- Returns:
- the index of a new or already existing method type reference item.
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newModule
Adds a module 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 forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
moduleName
- name of the module.- Returns:
- the index of a new or already existing module reference item.
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newPackage
Adds a package 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 forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
packageName
- name of the package in its internal form.- Returns:
- the index of a new or already existing module reference item.
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newHandle
Deprecated.this method is superseded bynewHandle(int, String, String, String, boolean)
.Adds a handle to the constant pool of the class being build. Does nothing if the constant pool already contains a similar item. This method is intended forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
tag
- the kind of this handle. Must beOpcodes.H_GETFIELD
,Opcodes.H_GETSTATIC
,Opcodes.H_PUTFIELD
,Opcodes.H_PUTSTATIC
,Opcodes.H_INVOKEVIRTUAL
,Opcodes.H_INVOKESTATIC
,Opcodes.H_INVOKESPECIAL
,Opcodes.H_NEWINVOKESPECIAL
orOpcodes.H_INVOKEINTERFACE
.owner
- the internal name of the field or method owner class (seeType.getInternalName()
).name
- the name of the field or method.descriptor
- the descriptor of the field or method.- Returns:
- the index of a new or already existing method type reference item.
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newHandle
Adds a handle to the constant pool of the class being build. Does nothing if the constant pool already contains a similar item. This method is intended forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
tag
- the kind of this handle. Must beOpcodes.H_GETFIELD
,Opcodes.H_GETSTATIC
,Opcodes.H_PUTFIELD
,Opcodes.H_PUTSTATIC
,Opcodes.H_INVOKEVIRTUAL
,Opcodes.H_INVOKESTATIC
,Opcodes.H_INVOKESPECIAL
,Opcodes.H_NEWINVOKESPECIAL
orOpcodes.H_INVOKEINTERFACE
.owner
- the internal name of the field or method owner class (seeType.getInternalName()
).name
- the name of the field or method.descriptor
- the descriptor of the field or method.isInterface
- true if the owner is an interface.- Returns:
- the index of a new or already existing method type reference item.
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newConstantDynamic
public int newConstantDynamic(String name, String descriptor, Handle bootstrapMethodHandle, Object... bootstrapMethodArguments) Adds a dynamic constant 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 forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
name
- name of the invoked method.descriptor
- field descriptor of the constant type.bootstrapMethodHandle
- the bootstrap method.bootstrapMethodArguments
- the bootstrap method constant arguments.- Returns:
- the index of a new or already existing dynamic constant reference item.
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newInvokeDynamic
public int newInvokeDynamic(String name, String descriptor, Handle bootstrapMethodHandle, Object... bootstrapMethodArguments) Adds an invokedynamic 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 forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
name
- name of the invoked method.descriptor
- descriptor of the invoke method.bootstrapMethodHandle
- the bootstrap method.bootstrapMethodArguments
- the bootstrap method constant arguments.- Returns:
- the index of a new or already existing invokedynamic reference item.
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newField
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 forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
owner
- the internal name of the field's owner class (seeType.getInternalName()
).name
- the field's name.descriptor
- the field's descriptor.- Returns:
- the index of a new or already existing field reference item.
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newMethod
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 forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
owner
- the internal name of the method's owner class (seeType.getInternalName()
).name
- the method's name.descriptor
- the method's descriptor.isInterface
- true ifowner
is an interface.- Returns:
- the index of a new or already existing method reference item.
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newNameType
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 forAttribute
sub classes, and is normally not needed by class generators or adapters.- Parameters:
name
- a name.descriptor
- a type descriptor.- Returns:
- the index of a new or already existing name and type item.
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getCommonSuperClass
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 (seeType.getInternalName()
).type2
- the internal name of another class (seeType.getInternalName()
).- Returns:
- the internal name of the common super class of the two given classes (see
Type.getInternalName()
).
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getClassLoader
Returns theClassLoader
to be used by the default implementation ofgetCommonSuperClass(String, String)
, that of thisClassWriter
's runtime type by default.- Returns:
- ClassLoader
-
newHandle(int, String, String, String, boolean)
.