Module java.base

Package java.lang.classfile^PREVIEW

Interface ClassReader

All Superinterfaces:

ConstantPoolPREVIEW, Iterable<PoolEntryPREVIEW>

public sealed interface ClassReader
extends ConstantPoolPREVIEW

ClassReader is a preview API of the Java platform.

Programs can only use ClassReader when preview features are enabled.

Preview features may be removed in a future release, or upgraded to permanent features of the Java platform.

Supports reading from a classfile. Methods are provided to read data of various numeric types (e.g., u2, u4) at a given offset within the classfile, copying raw bytes, and reading constant pool entries. Encapsulates additional reading context such as mappers for custom attributes and processing options.

Since:

22

Method Summary

Modifier and Type	Method	Description
int	classfileLength()	Returns the length of the classfile, in bytes.
boolean	compare(BufWriterPREVIEW bufWriter, int bufWriterOffset, int classReaderOffset, int length)	Compare a range of bytes from the classfile to a range of bytes within a BufWriterPREVIEW.
void	copyBytesTo(BufWriterPREVIEW buf, int offset, int len)	Copy a range of bytes from the classfile to a BufWriterPREVIEW
Function<Utf8EntryPREVIEW,AttributeMapperPREVIEW<?>>	customAttributes()	Returns the table of custom attribute mappers.
int	flags()	Returns the access flags for the class, as a bit mask.
byte[]	readBytes(int offset, int len)	Returns a copy of the bytes at the specified range in the classfile.
ClassEntryPREVIEW	readClassEntry(int offset)	Returns the class entry whose index is given at the specified offset within the classfile.
double	readDouble(int offset)	Returns the double value at the specified offset within the classfile.
PoolEntryPREVIEW	readEntry(int offset)	Returns the constant pool entry whose index is given at the specified offset within the classfile.
<T extends PoolEntryPREVIEW> T	readEntry(int offset, Class<T> cls)	Returns the constant pool entry of a given type whose index is given at the specified offset within the classfile.
PoolEntryPREVIEW	readEntryOrNull(int offset)	Returns the constant pool entry whose index is given at the specified offset within the classfile, or null if the index at the specified offset is zero.
float	readFloat(int offset)	Returns the float value at the specified offset within the classfile.
int	readInt(int offset)	Returns the signed int at the specified offset within the classfile.
long	readLong(int offset)	Returns the signed long at the specified offset within the classfile.
MethodHandleEntryPREVIEW	readMethodHandleEntry(int offset)	Returns the method handle entry whose index is given at the specified offset within the classfile.
ModuleEntryPREVIEW	readModuleEntry(int offset)	Returns the module entry whose index is given at the specified offset within the classfile.
NameAndTypeEntryPREVIEW	readNameAndTypeEntry(int offset)	Returns the name-and-type entry whose index is given at the specified offset within the classfile.
PackageEntryPREVIEW	readPackageEntry(int offset)	Returns the package entry whose index is given at the specified offset within the classfile.
int	readS1(int offset)	Returns the signed byte at the specified offset within the classfile.
int	readS2(int offset)	Returns the signed byte at the specified offset within the classfile.
int	readU1(int offset)	Returns the unsigned byte at the specified offset within the classfile.
int	readU2(int offset)	Returns the unsigned short at the specified offset within the classfile.
Utf8EntryPREVIEW	readUtf8Entry(int offset)	Returns the UTF8 entry whose index is given at the specified offset within the classfile.
Utf8EntryPREVIEW	readUtf8EntryOrNull(int offset)	Returns the UTF8 entry whose index is given at the specified offset within the classfile, or null if the index at the specified offset is zero.
int	skipAttributeHolder(int offset)	Returns the offset following the block of attributes starting at the specified position.
Optional<ClassEntryPREVIEW>	superclassEntry()	Returns the constant pool entry describing the name of the superclass, if any.
ClassEntryPREVIEW	thisClassEntry()	Returns the constant pool entry describing the name of class.
int	thisClassPos()	Returns the offset into the classfile of the this_class field.
Utf8EntryPREVIEW	utf8EntryByIndex(int index)	Returns the UTF8 constant pool entry at the given index of the constant pool.

Methods declared in interface java.lang.classfile.constantpool.ConstantPool^PREVIEW

bootstrapMethodCount, bootstrapMethodEntry, entryByIndex, iterator, size

Methods declared in interface java.lang.Iterable

forEach, spliterator

Method Details

customAttributes

Function<Utf8EntryPREVIEW,AttributeMapperPREVIEW<?>> customAttributes()

Returns the table of custom attribute mappers. This is derived from the processing option ClassFile.AttributeMapperOption^PREVIEW.

Returns:

the table of custom attribute mappers

flags

int flags()

Returns the access flags for the class, as a bit mask .

Returns:

the access flags for the class, as a bit mask

thisClassEntry

ClassEntryPREVIEW thisClassEntry()

Returns the constant pool entry describing the name of class.

Returns:

the constant pool entry describing the name of class

superclassEntry

Optional<ClassEntryPREVIEW> superclassEntry()

Returns the constant pool entry describing the name of the superclass, if any.

Returns:

the constant pool entry describing the name of the superclass, if any

thisClassPos

int thisClassPos()

Returns the offset into the classfile of the this_class field.

Returns:

the offset into the classfile of the this_class field

classfileLength

int classfileLength()

Returns the length of the classfile, in bytes.

Returns:

the length of the classfile, in bytes

skipAttributeHolder

int skipAttributeHolder(int offset)

Returns the offset following the block of attributes starting at the specified position.

Parameters:

offset - the offset into the classfile at which the attribute block starts

Returns:

the offset following the block of attributes starting at the specified position

utf8EntryByIndex

Utf8EntryPREVIEW utf8EntryByIndex(int index)

Returns the UTF8 constant pool entry at the given index of the constant pool. The given index must correspond to a valid constant pool index whose slot holds a UTF8 constant.

Parameters:

index - the index into the constant pool

Returns:

the UTF8 constant pool entry at the given index of the constant pool

readEntry

PoolEntryPREVIEW readEntry(int offset)

Returns the constant pool entry whose index is given at the specified offset within the classfile.

Parameters:

offset - the offset of the index within the classfile

Returns:

the constant pool entry whose index is given at the specified offset within the classfile

Throws:

ConstantPoolExceptionPREVIEW - if the index is out of range of the constant pool size, or zero

readEntry

<T extends PoolEntryPREVIEW> T readEntry(int offset,
 Class<T> cls)

Returns the constant pool entry of a given type whose index is given at the specified offset within the classfile.

Type Parameters:

T - the entry type

Parameters:

offset - the offset of the index within the classfile

cls - the entry type

Returns:

the constant pool entry of a given type whose index is given at the specified offset within the classfile

Throws:

ConstantPoolExceptionPREVIEW - if the index is out of range of the constant pool size, or zero, or the entry is not of the given type

readEntryOrNull

PoolEntryPREVIEW readEntryOrNull(int offset)

Returns the constant pool entry whose index is given at the specified offset within the classfile, or null if the index at the specified offset is zero.

Parameters:

offset - the offset of the index within the classfile

Returns:

the constant pool entry whose index is given at the specified offset within the classfile, or null if the index at the specified offset is zero

Throws:

ConstantPoolExceptionPREVIEW - if the index is out of range of the constant pool size

readUtf8Entry

Utf8EntryPREVIEW readUtf8Entry(int offset)

Returns the UTF8 entry whose index is given at the specified offset within the classfile.

Parameters:

offset - the offset of the index within the classfile

Returns:

the UTF8 entry whose index is given at the specified offset within the classfile

Throws:

ConstantPoolExceptionPREVIEW - if the index is out of range of the constant pool size, or zero, or the index does not correspond to a UTF8 entry

readUtf8EntryOrNull

Utf8EntryPREVIEW readUtf8EntryOrNull(int offset)

Returns the UTF8 entry whose index is given at the specified offset within the classfile, or null if the index at the specified offset is zero.

Parameters:

offset - the offset of the index within the classfile

Returns:

the UTF8 entry whose index is given at the specified offset within the classfile, or null if the index at the specified offset is zero

Throws:

ConstantPoolExceptionPREVIEW - if the index is out of range of the constant pool size, or the index does not correspond to a UTF8 entry

readModuleEntry

ModuleEntryPREVIEW readModuleEntry(int offset)

Returns the module entry whose index is given at the specified offset within the classfile.

Parameters:

offset - the offset of the index within the classfile

Returns:

the module entry whose index is given at the specified offset within the classfile

Throws:

ConstantPoolExceptionPREVIEW - if the index is out of range of the constant pool size, or zero, or the index does not correspond to a module entry

readPackageEntry

PackageEntryPREVIEW readPackageEntry(int offset)

Returns the package entry whose index is given at the specified offset within the classfile.

Parameters:

offset - the offset of the index within the classfile

Returns:

the package entry whose index is given at the specified offset within the classfile

Throws:

ConstantPoolExceptionPREVIEW - if the index is out of range of the constant pool size, or zero, or the index does not correspond to a package entry

readClassEntry

ClassEntryPREVIEW readClassEntry(int offset)

Returns the class entry whose index is given at the specified offset within the classfile.

Parameters:

offset - the offset of the index within the classfile

Returns:

the class entry whose index is given at the specified offset within the classfile

Throws:

ConstantPoolExceptionPREVIEW - if the index is out of range of the constant pool size, or zero, or the index does not correspond to a class entry

readNameAndTypeEntry

NameAndTypeEntryPREVIEW readNameAndTypeEntry(int offset)

Returns the name-and-type entry whose index is given at the specified offset within the classfile.

Parameters:

offset - the offset of the index within the classfile

Returns:

the name-and-type entry whose index is given at the specified offset within the classfile

Throws:

ConstantPoolExceptionPREVIEW - if the index is out of range of the constant pool size, or zero, or the index does not correspond to a name-and-type entry

readMethodHandleEntry

MethodHandleEntryPREVIEW readMethodHandleEntry(int offset)

Returns the method handle entry whose index is given at the specified offset within the classfile.

Parameters:

offset - the offset of the index within the classfile

Returns:

the method handle entry whose index is given at the specified offset within the classfile

Throws:

ConstantPoolExceptionPREVIEW - if the index is out of range of the constant pool size, or zero, or the index does not correspond to a method handle entry

readU1

int readU1(int offset)

Returns the unsigned byte at the specified offset within the classfile.

Parameters:

offset - the offset within the classfile

Returns:

the unsigned byte at the specified offset within the classfile

readU2

int readU2(int offset)

Returns the unsigned short at the specified offset within the classfile.

Parameters:

offset - the offset within the classfile

Returns:

the unsigned short at the specified offset within the classfile

readS1

int readS1(int offset)

Returns the signed byte at the specified offset within the classfile.

Parameters:

offset - the offset within the classfile

Returns:

the signed byte at the specified offset within the classfile

readS2

int readS2(int offset)

Returns the signed byte at the specified offset within the classfile.

Parameters:

offset - the offset within the classfile

Returns:

the signed byte at the specified offset within the classfile

readInt

int readInt(int offset)

Returns the signed int at the specified offset within the classfile.

Parameters:

offset - the offset within the classfile

Returns:

the signed int at the specified offset within the classfile

readLong

long readLong(int offset)

Returns the signed long at the specified offset within the classfile.

Parameters:

offset - the offset within the classfile

Returns:

the signed long at the specified offset within the classfile

readFloat

float readFloat(int offset)

Returns the float value at the specified offset within the classfile.

Parameters:

offset - the offset within the classfile

Returns:

the float value at the specified offset within the classfile

readDouble

double readDouble(int offset)

Returns the double value at the specified offset within the classfile.

Parameters:

offset - the offset within the classfile

Returns:

the double value at the specified offset within the classfile

readBytes

byte[] readBytes(int offset,
 int len)

Returns a copy of the bytes at the specified range in the classfile.

Parameters:

offset - the offset within the classfile

len - the length of the range

Returns:

a copy of the bytes at the specified range in the classfile

copyBytesTo

void copyBytesTo(BufWriterPREVIEW buf,
 int offset,
 int len)

Copy a range of bytes from the classfile to a BufWriter^PREVIEW

Parameters:

buf - the BufWriter^PREVIEW

offset - the offset within the classfile

len - the length of the range

compare

boolean compare(BufWriterPREVIEW bufWriter,
 int bufWriterOffset,
 int classReaderOffset,
 int length)

Compare a range of bytes from the classfile to a range of bytes within a BufWriter^PREVIEW.

Parameters:

bufWriter - the BufWriter^PREVIEW

bufWriterOffset - the offset within the BufWriter^PREVIEW

classReaderOffset - the offset within the classfile

length - the length of the range

Returns:

whether the two ranges were identical