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.
CodeStackTrackerPREVIEW is a CodeTransformPREVIEW 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

  • Method Details

    • of

      static CodeStackTrackerPREVIEW of(TypeKindPREVIEW... initialStack)
      Creates new instance of CodeStackTrackerPREVIEW initialized with provided stack items.
      Parameters:
      initialStack - initial stack content
      Returns:
      new instance of CodeStackTrackerPREVIEW

    • stack

      Optional<Collection<TypeKindPREVIEW>> stack()
      Returns Collection of TypeKindPREVIEW 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 LabelPREVIEW used as target of a branch instruction from existing code with known stack (forward branch target), or by binding of a LabelPREVIEW 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