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. 
final class com.google.common.collect.MapMakerInternalMap$KeyIterator extends com.google.common.collect.MapMakerInternalMap<K, V, E, S>.HashIterator<K>
  minor version: 0
  major version: 59
  flags: flags: (0x0030) ACC_FINAL, ACC_SUPER
  this_class: com.google.common.collect.MapMakerInternalMap$KeyIterator
  super_class: com.google.common.collect.MapMakerInternalMap$HashIterator
{
  final com.google.common.collect.MapMakerInternalMap this$0;
    descriptor: Lcom/google/common/collect/MapMakerInternalMap;
    flags: (0x1010) ACC_FINAL, ACC_SYNTHETIC

  void <init>(com.google.common.collect.MapMakerInternalMap);
    descriptor: (Lcom/google/common/collect/MapMakerInternalMap;)V
    flags: (0x0000) 
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // com.google.common.collect.MapMakerInternalMap$KeyIterator this
         0: .line 2607
            aload 0 /* this */
            aload 1
            putfield com.google.common.collect.MapMakerInternalMap$KeyIterator.this$0:Lcom/google/common/collect/MapMakerInternalMap;
            aload 0 /* this */
            aload 1
            invokespecial com.google.common.collect.MapMakerInternalMap$HashIterator.<init>:(Lcom/google/common/collect/MapMakerInternalMap;)V
            return
        end local 0 // com.google.common.collect.MapMakerInternalMap$KeyIterator this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/MapMakerInternalMap$KeyIterator;
    MethodParameters:
        Name  Flags
      this$0  final

  public K next();
    descriptor: ()Ljava/lang/Object;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // com.google.common.collect.MapMakerInternalMap$KeyIterator this
         0: .line 2611
            aload 0 /* this */
            invokevirtual com.google.common.collect.MapMakerInternalMap$KeyIterator.nextEntry:()Lcom/google/common/collect/MapMakerInternalMap$WriteThroughEntry;
            invokevirtual com.google.common.collect.MapMakerInternalMap$WriteThroughEntry.getKey:()Ljava/lang/Object;
            areturn
        end local 0 // com.google.common.collect.MapMakerInternalMap$KeyIterator this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/collect/MapMakerInternalMap$KeyIterator;
    Signature: ()TK;
}
Signature: Lcom/google/common/collect/MapMakerInternalMap<TK;TV;TE;TS;>.HashIterator<TK;>;
SourceFile: "MapMakerInternalMap.java"
NestHost: com.google.common.collect.MapMakerInternalMap
InnerClasses:
  abstract HashIterator = com.google.common.collect.MapMakerInternalMap$HashIterator of com.google.common.collect.MapMakerInternalMap
  final KeyIterator = com.google.common.collect.MapMakerInternalMap$KeyIterator of com.google.common.collect.MapMakerInternalMap
  final WriteThroughEntry = com.google.common.collect.MapMakerInternalMap$WriteThroughEntry of com.google.common.collect.MapMakerInternalMap