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 Details

    • customAttributes

      Returns the table of custom attribute mappers. This is derived from the processing option ClassFile.AttributeMapperOptionPREVIEW.
      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
    • classfileLength

      int classfileLength()
      Returns the length of the classfile, in bytes.
      Returns:
      the length of the classfile, in bytes
    • readEntry

      PoolEntryPREVIEW readEntry(int offset)
      Returns the constant pool entry whose index is given at the specified offset within the classfile.
      API Note:
      If only a particular type of entry is expected, use readEntry(int, Class).
      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.
      API Note:
      If only a particular type of entry is expected, use readEntryOrNull(int, Class).
      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
    • readEntryOrNull

      <T extends PoolEntryPREVIEW> T readEntryOrNull(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, or null if the index at the specified offset is zero.
      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, 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 zero, or the entry is not of the given type
      Since:
      23
    • 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 BufWriterPREVIEW
      Parameters:
      buf - the BufWriterPREVIEW
      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 BufWriterPREVIEW.
      Parameters:
      bufWriter - the BufWriterPREVIEW
      bufWriterOffset - the offset within the BufWriterPREVIEW
      classReaderOffset - the offset within the classfile
      length - the length of the range
      Returns:
      whether the two ranges were identical