Module java.base

Package java.lang.classfile.components^PREVIEW

Interface CodeStackTracker

All Superinterfaces:

ClassFileTransformPREVIEW<CodeTransformPREVIEW,CodeElementPREVIEW,CodeBuilderPREVIEW>, CodeTransformPREVIEW

public sealed interface CodeStackTracker
extends CodeTransformPREVIEW

CodeStackTracker is a preview API of the Java platform.

Programs can only use CodeStackTracker when preview features are enabled.

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

CodeStackTracker^PREVIEW is a CodeTransform^PREVIEW tracking stack content and calculating max stack size.

Sample use:

    var stackTracker = CodeStackTracker.of();
    codeBuilder.transforming(stackTracker, trackedBuilder -> {
        trackedBuilder.aload(0);
        trackedBuilder.lconst_0();
        trackedBuilder.ifThen(...);
        ...
        var stack = stackTracker.stack().get();
        int maxStack = stackTracker.maxStackSize().get();
    });

Since:

22

Nested Class Summary

Nested classes/interfaces declared in interface java.lang.classfile.ClassFileTransform^PREVIEW

ClassFileTransform.ResolvedTransformPREVIEW<E extends ClassFileElementPREVIEW>

Field Summary

Fields declared in interface java.lang.classfile.CodeTransform^PREVIEW

ACCEPT_ALL

Method Summary

Modifier and Type	Method	Description
Optional<Integer>	maxStackSize()	Returns tracked max stack size.
static CodeStackTrackerPREVIEW	of(TypeKindPREVIEW... initialStack)	Creates new instance of CodeStackTrackerPREVIEW initialized with provided stack items.
Optional<Collection<TypeKindPREVIEW>>	stack()	Returns Collection of TypeKindPREVIEW representing current stack.

Methods declared in interface java.lang.classfile.ClassFileTransform^PREVIEW

accept, atEnd, atStart

Methods declared in interface java.lang.classfile.CodeTransform^PREVIEW

andThen, resolve

Method Details

of

static CodeStackTrackerPREVIEW of(TypeKindPREVIEW... initialStack)

Creates new instance of CodeStackTracker^PREVIEW initialized with provided stack items.

Parameters:

initialStack - initial stack content

Returns:

new instance of CodeStackTracker^PREVIEW

stack

Optional<Collection<TypeKindPREVIEW>> stack()

Returns Collection of TypeKind^PREVIEW representing current stack. Returns an empty Optional when the Stack content is unknown (right after xRETURN, ATHROW, GOTO, GOTO_W, LOOKUPSWITCH, TABLESWITCH instructions).

Temporary unknown stack content can be recovered by binding of a Label^PREVIEW used as target of a branch instruction from existing code with known stack (forward branch target), or by binding of a Label^PREVIEW defining an exception handler (exception handler code start).

Returns:

actual stack content, or an empty Optional if unknown

maxStackSize

Optional<Integer> maxStackSize()

Returns tracked max stack size. Returns an empty Optional when max stack size tracking has been lost.

Max stack size tracking is permanently lost when a stack instruction appears and the actual stack content is unknown.

Returns:

tracked max stack size, or an empty Optional if tracking has been lost