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. 
interface com.google.protobuf.MapField$Converter<K, V>
  minor version: 0
  major version: 59
  flags: flags: (0x0600) ACC_INTERFACE, ACC_ABSTRACT
  this_class: com.google.protobuf.MapField$Converter
  super_class: java.lang.Object
{
  public abstract com.google.protobuf.Message convertKeyAndValueToMessage(K, V);
    descriptor: (Ljava/lang/Object;Ljava/lang/Object;)Lcom/google/protobuf/Message;
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT
    Signature: (TK;TV;)Lcom/google/protobuf/Message;
    MethodParameters:
       Name  Flags
      key    
      value  

  public abstract void convertMessageToKeyAndValue(com.google.protobuf.Message, java.util.Map<K, V>);
    descriptor: (Lcom/google/protobuf/Message;Ljava/util/Map;)V
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT
    Signature: (Lcom/google/protobuf/Message;Ljava/util/Map<TK;TV;>;)V
    MethodParameters:
         Name  Flags
      message  
      map      

  public abstract com.google.protobuf.Message getMessageDefaultInstance();
    descriptor: ()Lcom/google/protobuf/Message;
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT
}
Signature: <K:Ljava/lang/Object;V:Ljava/lang/Object;>Ljava/lang/Object;
SourceFile: "MapField.java"
NestHost: com.google.protobuf.MapField
InnerClasses:
  private abstract Converter = com.google.protobuf.MapField$Converter of com.google.protobuf.MapField