https://lucene.apache.org/lucene-parent/lucene-join: Lucene Join Module (The Apache Software Foundation) 
interface org.apache.lucene.search.join.DocValuesTermsCollector$Function<R>
  minor version: 0
  major version: 59
  flags: flags: (0x0600) ACC_INTERFACE, ACC_ABSTRACT
  this_class: org.apache.lucene.search.join.DocValuesTermsCollector$Function
  super_class: java.lang.Object
{
  public abstract R apply(org.apache.lucene.index.LeafReader);
    descriptor: (Lorg/apache/lucene/index/LeafReader;)Ljava/lang/Object;
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT
    Exceptions:
      throws java.io.IOException
    Signature: (Lorg/apache/lucene/index/LeafReader;)TR;
    MethodParameters:
      Name  Flags
      t     
}
Signature: <R:Ljava/lang/Object;>Ljava/lang/Object;
SourceFile: "DocValuesTermsCollector.java"
NestHost: org.apache.lucene.search.join.DocValuesTermsCollector
InnerClasses:
  abstract Function = org.apache.lucene.search.join.DocValuesTermsCollector$Function of org.apache.lucene.search.join.DocValuesTermsCollector
    RuntimeVisibleAnnotations: 
      java.lang.FunctionalInterface()