https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. 
class com.google.common.collect.FilteredEntryMultimap$AsMap$1KeySetImpl extends com.google.common.collect.Maps$KeySet<K, java.util.Collection<V>>
  minor version: 0
  major version: 59
  flags: flags: (0x0020) ACC_SUPER
  this_class: com.google.common.collect.FilteredEntryMultimap$AsMap$1KeySetImpl
  super_class: com.google.common.collect.Maps$KeySet
{
  final com.google.common.collect.FilteredEntryMultimap$AsMap this$1;
    descriptor: Lcom/google/common/collect/FilteredEntryMultimap$AsMap;
    flags: (0x1010) ACC_FINAL, ACC_SYNTHETIC

  void <init>(com.google.common.collect.FilteredEntryMultimap$AsMap);
    descriptor: (Lcom/google/common/collect/FilteredEntryMultimap$AsMap;)V
    flags: (0x0000) 
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // com.google.common.collect.FilteredEntryMultimap$AsMap$1KeySetImpl this
         0: .line 220
            aload 0 /* this */
            aload 1
            putfield com.google.common.collect.FilteredEntryMultimap$AsMap$1KeySetImpl.this$1:Lcom/google/common/collect/FilteredEntryMultimap$AsMap;
         1: .line 221
            aload 0 /* this */
            aload 1
            invokespecial com.google.common.collect.Maps$KeySet.<init>:(Ljava/util/Map;)V
         2: .line 222
            return
        end local 0 // com.google.common.collect.FilteredEntryMultimap$AsMap$1KeySetImpl this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    3     0  this  Lcom/google/common/collect/FilteredEntryMultimap$AsMap$1KeySetImpl;
    MethodParameters:
        Name  Flags
      this$0  final

  public boolean removeAll(java.util.Collection<?>);
    descriptor: (Ljava/util/Collection;)Z
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // com.google.common.collect.FilteredEntryMultimap$AsMap$1KeySetImpl this
        start local 1 // java.util.Collection c
         0: .line 226
            aload 0 /* this */
            getfield com.google.common.collect.FilteredEntryMultimap$AsMap$1KeySetImpl.this$1:Lcom/google/common/collect/FilteredEntryMultimap$AsMap;
            invokestatic com.google.common.collect.FilteredEntryMultimap$AsMap.access$2:(Lcom/google/common/collect/FilteredEntryMultimap$AsMap;)Lcom/google/common/collect/FilteredEntryMultimap;
            aload 1 /* c */
            invokestatic com.google.common.base.Predicates.in:(Ljava/util/Collection;)Lcom/google/common/base/Predicate;
            invokestatic com.google.common.collect.Maps.keyPredicateOnEntries:(Lcom/google/common/base/Predicate;)Lcom/google/common/base/Predicate;
            invokevirtual com.google.common.collect.FilteredEntryMultimap.removeEntriesIf:(Lcom/google/common/base/Predicate;)Z
            ireturn
        end local 1 // java.util.Collection c
        end local 0 // com.google.common.collect.FilteredEntryMultimap$AsMap$1KeySetImpl this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/FilteredEntryMultimap$AsMap$1KeySetImpl;
            0    1     1     c  Ljava/util/Collection<*>;
    Signature: (Ljava/util/Collection<*>;)Z
    MethodParameters:
      Name  Flags
      c     

  public boolean retainAll(java.util.Collection<?>);
    descriptor: (Ljava/util/Collection;)Z
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // com.google.common.collect.FilteredEntryMultimap$AsMap$1KeySetImpl this
        start local 1 // java.util.Collection c
         0: .line 231
            aload 0 /* this */
            getfield com.google.common.collect.FilteredEntryMultimap$AsMap$1KeySetImpl.this$1:Lcom/google/common/collect/FilteredEntryMultimap$AsMap;
            invokestatic com.google.common.collect.FilteredEntryMultimap$AsMap.access$2:(Lcom/google/common/collect/FilteredEntryMultimap$AsMap;)Lcom/google/common/collect/FilteredEntryMultimap;
            aload 1 /* c */
            invokestatic com.google.common.base.Predicates.in:(Ljava/util/Collection;)Lcom/google/common/base/Predicate;
            invokestatic com.google.common.base.Predicates.not:(Lcom/google/common/base/Predicate;)Lcom/google/common/base/Predicate;
            invokestatic com.google.common.collect.Maps.keyPredicateOnEntries:(Lcom/google/common/base/Predicate;)Lcom/google/common/base/Predicate;
            invokevirtual com.google.common.collect.FilteredEntryMultimap.removeEntriesIf:(Lcom/google/common/base/Predicate;)Z
            ireturn
        end local 1 // java.util.Collection c
        end local 0 // com.google.common.collect.FilteredEntryMultimap$AsMap$1KeySetImpl this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/FilteredEntryMultimap$AsMap$1KeySetImpl;
            0    1     1     c  Ljava/util/Collection<*>;
    Signature: (Ljava/util/Collection<*>;)Z
    MethodParameters:
      Name  Flags
      c     

  public boolean remove(java.lang.Object);
    descriptor: (Ljava/lang/Object;)Z
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // com.google.common.collect.FilteredEntryMultimap$AsMap$1KeySetImpl this
        start local 1 // java.lang.Object o
         0: .line 236
            aload 0 /* this */
            getfield com.google.common.collect.FilteredEntryMultimap$AsMap$1KeySetImpl.this$1:Lcom/google/common/collect/FilteredEntryMultimap$AsMap;
            aload 1 /* o */
            invokevirtual com.google.common.collect.FilteredEntryMultimap$AsMap.remove:(Ljava/lang/Object;)Ljava/util/Collection;
            ifnull 1
            iconst_1
            ireturn
      StackMap locals:
      StackMap stack:
         1: iconst_0
            ireturn
        end local 1 // java.lang.Object o
        end local 0 // com.google.common.collect.FilteredEntryMultimap$AsMap$1KeySetImpl this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    2     0  this  Lcom/google/common/collect/FilteredEntryMultimap$AsMap$1KeySetImpl;
            0    2     1     o  Ljava/lang/Object;
    RuntimeVisibleTypeAnnotations: 
      METHOD_FORMAL_PARAMETER
        org.checkerframework.checker.nullness.qual.Nullable()
    MethodParameters:
      Name  Flags
      o     
}
Signature: Lcom/google/common/collect/Maps$KeySet<TK;Ljava/util/Collection<TV;>;>;
SourceFile: "FilteredEntryMultimap.java"
EnclosingMethod: com.google.common.collect.FilteredEntryMultimap$AsMap.createKeySet:()Ljava/util/Set;
NestHost: com.google.common.collect.FilteredEntryMultimap
InnerClasses:
  AsMap = com.google.common.collect.FilteredEntryMultimap$AsMap of com.google.common.collect.FilteredEntryMultimap
  KeySetImpl = com.google.common.collect.FilteredEntryMultimap$AsMap$1KeySetImpl
  KeySet = com.google.common.collect.Maps$KeySet of com.google.common.collect.Maps
  public abstract Entry = java.util.Map$Entry of java.util.Map