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:

• StackMapTableAttribute
• ClassFile.DeadCodeOption

Nested Class Summary

Nested classes/interfaces declared in class Enum

Enum.EnumDesc<E>

Modifier and Type	Class	Description
static final class	Enum.EnumDesc<E extends Enum<E>>	A nominal descriptor for an enum constant.

Enum Constant Summary

Enum Constants

Enum Constant	Description
DROP_STACK_MAPS	Do not run stack map generation.
GENERATE_STACK_MAPS	Forces running stack map generation.
STACK_MAPS_WHEN_REQUIRED	Generate stack maps or reuse existing ones if compatible.

Method Summary

Modifier and Type	Method	Description
static ClassFile.StackMapsOption	valueOf(String name)	Returns the enum constant of this class with the specified name.
static ClassFile.StackMapsOption[]	values()	Returns an array containing the constants of this enum class, in the order they are declared.

Methods declared in class Enum

clone, compareTo, describeConstable, equals, finalize, getDeclaringClass, hashCode, name, ordinal, toString, valueOf

Modifier and Type	Method	Description
protected final Object	clone()	Throws CloneNotSupportedException.
final int	compareTo(ClassFile.StackMapsOption o)	Compares this enum with the specified object for order.
final Optional<Enum.EnumDesc<ClassFile.StackMapsOption>>	describeConstable()	Returns an enum descriptor EnumDesc for this instance, if one can be constructed, or an empty Optional if one cannot be.
final boolean	equals(Object other)	Returns true if the specified object is equal to this enum constant.
protected final void	finalize()	Deprecated, for removal: This API element is subject to removal in a future version. Finalization has been deprecated for removal.
final Class<ClassFile.StackMapsOption>	getDeclaringClass()	Returns the Class object corresponding to this enum constant's enum type.
final int	hashCode()	Returns a hash code for this enum constant.
final String	name()	Returns the name of this enum constant, exactly as declared in its enum declaration.
final int	ordinal()	Returns the ordinal of this enumeration constant (its position in its enum declaration, where the initial constant is assigned an ordinal of zero).
String	toString()	Returns the name of this enum constant, as contained in the declaration.
static <T extends Enum<T>> T	valueOf(Class<T> enumClass, String name)	Returns the enum constant of the specified enum class with the specified name.

Methods declared in class Object

getClass, notify, notifyAll, wait, wait, wait

Modifier and Type	Method	Description
final Class<?>	getClass()	Returns the runtime class of this Object.
final void	notify()	Wakes up a single thread that is waiting on this object's monitor.
final void	notifyAll()	Wakes up all threads that are waiting on this object's monitor.
final void	wait()	Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
final void	wait(long timeoutMillis)	Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
final void	wait(long timeoutMillis, int nanos)	Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

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