Package org.codehaus.groovy.transform

# Class SingletonASTStubber

java.lang.Object
org.codehaus.groovy.transform.AbstractASTTransformation
org.codehaus.groovy.transform.SingletonASTStubber

All Implemented Interfaces:
  `ASTTransformation`, `ErrorCollecting`

public class SingletonASTStubber extends AbstractASTTransformation
Joint-compilation stubber for `Singleton`. Emits the public static `getInstance()` method (or `getXxx()` for a custom property name) so Java consumers can call `MyClass.getInstance()` against the joint-compilation stub.

The placeholder body returns `null`; the full `SingletonASTTransformation` at CANONICALIZATION recognises the stubber metadata and replaces the body with the real implementation (which dereferences the singleton field, optionally with double-checked locking when `lazy = true`).

The corresponding singleton field is intentionally not emitted from the stubber. For the default `lazy = false` configuration the runtime field is public static final and Java callers could read it directly; emitting it here would risk a duplicate-add at CANONICALIZATION, and the `getInstance()` accessor is the canonical Java idiom. Adding the field could be a follow-up if the spike's experience suggests Java consumers commonly want field-level access.

Since:
  6.0.0

- ## Field Summary

  ### Fields inherited from class org.codehaus.groovy.transform.AbstractASTTransformation

  `RETENTION_CLASSNODE, sourceUnit`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `SingletonASTStubber()`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `visit(ASTNode[] nodes, SourceUnit source)`
  The method is invoked when an AST Transformation is active.

  ### Methods inherited from class org.codehaus.groovy.transform.AbstractASTTransformation

  `addError, checkIncludeExcludeUndefinedAware, checkIncludeExcludeUndefinedAware, checkNotInterface, checkPropertyList, checkPropertyList, checkPropertyList, copyAnnotatedNodeAnnotations, copyAnnotatedNodeAnnotations, deemedInternal, deemedInternalName, getAnnotationName, getMemberClassList, getMemberClassValue, getMemberClassValue, getMemberIntValue, getMemberStringList, getMemberStringValue, getMemberStringValue, getMemberValue, hasAnnotation, init, markAsInternal, memberHasValue, shouldSkip, shouldSkip, shouldSkip, shouldSkipOnDescriptorUndefinedAware, shouldSkipUndefinedAware, shouldSkipUndefinedAware, shouldSkipUndefinedAware, tokenize`

  ### Methods inherited from class java.lang.Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Constructor Details

  - ### SingletonASTStubber

    public SingletonASTStubber()

- ## Method Details

  - ### visit

    public void visit(ASTNode[] nodes, SourceUnit source)
    Description copied from interface: `ASTTransformation`
    The method is invoked when an AST Transformation is active. For local transformations, it is invoked once each time the local annotation is encountered. For global transformations, it is invoked once for every source unit, which is typically a source file.
    Parameters:
      `nodes` - The ASTnodes when the call was triggered. Element 0 is the AnnotationNode that triggered this annotation to be activated. Element 1 is the AnnotatedNode decorated, such as a MethodNode or ClassNode. For global transformations it is usually safe to ignore this parameter.
      `source` - The source unit being compiled. The source unit may contain several classes. For global transformations, information about the AST can be retrieved from this object.