https://lucene.apache.org/lucene-parent/lucene-core: Apache Lucene Java Core (The Apache Software Foundation) 
public interface org.apache.lucene.index.IndexReader$ClosedListener
  minor version: 0
  major version: 59
  flags: flags: (0x0601) ACC_PUBLIC, ACC_INTERFACE, ACC_ABSTRACT
  this_class: org.apache.lucene.index.IndexReader$ClosedListener
  super_class: java.lang.Object
{
  public abstract void onClose(org.apache.lucene.index.IndexReader$CacheKey);
    descriptor: (Lorg/apache/lucene/index/IndexReader$CacheKey;)V
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT
    Exceptions:
      throws java.io.IOException
    MethodParameters:
      Name  Flags
      key   
}
SourceFile: "IndexReader.java"
NestHost: org.apache.lucene.index.IndexReader
InnerClasses:
  public final CacheKey = org.apache.lucene.index.IndexReader$CacheKey of org.apache.lucene.index.IndexReader
  public abstract ClosedListener = org.apache.lucene.index.IndexReader$ClosedListener of org.apache.lucene.index.IndexReader
    RuntimeVisibleAnnotations: 
      java.lang.FunctionalInterface()