Enum Class ClassFile.StackMapsOption

java.lang.Object
java.lang.Enum<ClassFile.StackMapsOption>
java.lang.classfile.ClassFile.StackMapsOption
All Implemented Interfaces:
Serializable, ClassFile.Option, Comparable<ClassFile.StackMapsOption>, Constable
Enclosing interface:
ClassFile
public static enum ClassFile.StackMapsOption extends Enum<ClassFile.StackMapsOption> implements ClassFile.Option
The option describing whether to generate stack maps. The default is STACK_MAPS_WHEN_REQUIRED to generate stack maps or reuse existing ones if compatible.

The StackMapTableAttribute is a derived property from a Code attribute to allow a Java Virtual Machine to perform verification in one pass. Thus, it is not modeled as part of a CodeModel, but computed on-demand instead via stack maps generation.

Stack map generation may fail with an IllegalArgumentException if there is unreachable code or legacy jump routine instructions. When DROP_STACK_MAPS option is used, users can provide their own stack maps by supplying a StackMapTableAttribute to a CodeBuilder.

See Java Virtual Machine Specification:
4.10.1 Verification by Type Checking
Since:
24
See Also:

  • Enum Constant Details

    • STACK_MAPS_WHEN_REQUIRED

      public static final ClassFile.StackMapsOption STACK_MAPS_WHEN_REQUIRED
      Generate stack maps or reuse existing ones if compatible. Stack maps are present on major versions 50 or above. For these versions, CodeBuilder tries to reuse compatible stack maps information if the code array and exception handlers are still compatible after a transformation; otherwise, it runs stack map generation. However, it does not fail fast if the major version is 50, which allows jump subroutine instructions that are incompatible with stack maps to exist in the code array.

    • GENERATE_STACK_MAPS

      public static final ClassFile.StackMapsOption GENERATE_STACK_MAPS
      Forces running stack map generation. This runs stack map generation unconditionally and fails fast if the generation fails due to any reason.

    • DROP_STACK_MAPS

      public static final ClassFile.StackMapsOption DROP_STACK_MAPS
      Do not run stack map generation. Users must supply their own StackMapTableAttribute to a CodeBuilder if the code has branches or exception handlers; otherwise, the generated code will fail verification (JVMS 4.10.1).

      This option is required for user-supplied StackMapTableAttribute to be respected. Stack maps on an existing Code attribute can be reused as below with this option: 

      CodeAttribute code = method.findAttribute(Attributes.code()).orElseThrow();
// Note that StackMapTable may be absent, representing code with no branching
code.findAttribute(Attributes.stackMapTable()).ifPresent(cob);

  • Method Details

    • values

      public static ClassFile.StackMapsOption[] values()
      Returns an array containing the constants of this enum class, in the order they are declared.
      Returns:
      an array containing the constants of this enum class, in the order they are declared

    • valueOf

      public static ClassFile.StackMapsOption valueOf(String name)
      Returns the enum constant of this class with the specified name. The string must match exactly an identifier used to declare an enum constant in this class. (Extraneous whitespace characters are not permitted.)
      Parameters:
      name - the name of the enum constant to be returned.
      Returns:
      the enum constant with the specified name
      Throws:
      IllegalArgumentException - if this enum class has no constant with the specified name
      NullPointerException - if the argument is null