https://developers.google.com/protocol-buffers/protobuf-java/: Core Protocol Buffers library. Protocol Buffers are a way of encoding structured data in an efficient yet extensible format. 
class com.google.protobuf.SmallSortedMap$EmptySet$2 implements java.lang.Iterable<java.lang.Object>
  minor version: 0
  major version: 59
  flags: flags: (0x0020) ACC_SUPER
  this_class: com.google.protobuf.SmallSortedMap$EmptySet$2
  super_class: java.lang.Object
{
  void <init>();
    descriptor: ()V
    flags: (0x0000) 
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // com.google.protobuf.SmallSortedMap$EmptySet$2 this
         0: .line 651
            aload 0 /* this */
            invokespecial java.lang.Object.<init>:()V
            return
        end local 0 // com.google.protobuf.SmallSortedMap$EmptySet$2 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/protobuf/SmallSortedMap$EmptySet$2;

  public java.util.Iterator<java.lang.Object> iterator();
    descriptor: ()Ljava/util/Iterator;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // com.google.protobuf.SmallSortedMap$EmptySet$2 this
         0: .line 654
            getstatic com.google.protobuf.SmallSortedMap$EmptySet.ITERATOR:Ljava/util/Iterator;
            areturn
        end local 0 // com.google.protobuf.SmallSortedMap$EmptySet$2 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/protobuf/SmallSortedMap$EmptySet$2;
    Signature: ()Ljava/util/Iterator<Ljava/lang/Object;>;
}
Signature: Ljava/lang/Object;Ljava/lang/Iterable<Ljava/lang/Object;>;
SourceFile: "SmallSortedMap.java"
EnclosingMethod: com.google.protobuf.SmallSortedMap$EmptySet
NestHost: com.google.protobuf.SmallSortedMap
InnerClasses:
  private EmptySet = com.google.protobuf.SmallSortedMap$EmptySet of com.google.protobuf.SmallSortedMap
  com.google.protobuf.SmallSortedMap$EmptySet$2