Akka Protobuf V3

import akka.protobufv3.internal.Message;
import akka.protobufv3.internal.ByteString;
import akka.protobufv3.internal.CodedInputStream;
import akka.protobufv3.internal.CodedOutputStream;

import akka.protobufv3.internal.{Message, ByteString, CodedInputStream, CodedOutputStream}

import akka.protobufv3.internal.*;

// Create a ByteString from UTF-8 text
ByteString data = ByteString.copyFromUtf8("Hello, Protocol Buffers!");

// Convert back to string
String text = data.toStringUtf8();

// Serialize ByteString to byte array
byte[] bytes = data.toByteArray();

// Create ByteString from byte array
ByteString restored = ByteString.copyFrom(bytes);

// Parse a message from bytes (example with a hypothetical UserMessage)
// UserMessage message = UserMessage.parseFrom(bytes);

interface Message extends MessageLite, MessageOrBuilder {
    // Core message interface with full functionality
}

interface MessageLite {
    // Lite message interface with minimal functionality  
}

abstract class AbstractMessage implements Message {
    // Partial implementation of Message interface
}

abstract class GeneratedMessageV3 extends AbstractMessage {
    // Base class for generated protocol buffer messages
}

class ByteString {
    static ByteString copyFrom(byte[] bytes);
    static ByteString copyFromUtf8(String text);
    byte[] toByteArray();
    String toStringUtf8();
    ByteString substring(int beginIndex);
    ByteString concat(ByteString other);
}

class CodedInputStream {
    static CodedInputStream newInstance(byte[] buf);
    static CodedInputStream newInstance(InputStream input);
    // Read methods for various protobuf types
}

class CodedOutputStream {
    static CodedOutputStream newInstance(byte[] flatArray);
    static CodedOutputStream newInstance(OutputStream output);
    // Write methods for various protobuf types
}

class Descriptors {
    static class Descriptor {
        // Describes a message type
        String getName();
        String getFullName();
        List<FieldDescriptor> getFields();
    }
    
    static class FieldDescriptor {
        // Describes a field in a message
        String getName();
        FieldType getType();
        boolean isRepeated();
    }
    
    static class FileDescriptor {
        // Describes a .proto file
        String getName();
        List<Descriptor> getMessageTypes();
    }
}

class DynamicMessage implements Message {
    // Can represent arbitrary message types given a Descriptor
    static DynamicMessage newBuilder(Descriptor type);
}

class Timestamp implements Message {
    // Represents a point in time
    long getSeconds();
    int getNanos();
    static Builder newBuilder();
}

class Duration implements Message {
    // Represents a span of time
    long getSeconds();  
    int getNanos();
    static Builder newBuilder();
}

class Any implements Message {
    // Contains an arbitrary serialized message
    String getTypeUrl();
    ByteString getValue();
    static Builder newBuilder();
}

class JsonFormat {
    static class Parser {
        // Parse JSON to protobuf message
        Parser ignoringUnknownFields();
        Parser usingTypeRegistry(TypeRegistry registry);
        void merge(String json, Message.Builder builder);
    }
    
    static class Printer {
        // Convert protobuf message to JSON
        Printer includingDefaultValueFields();
        Printer preservingProtoFieldNames(); 
        String print(MessageOrBuilder message);
    }
    
    static Parser parser();
    static Printer printer();
}

class TextFormat {
    // Utilities for converting messages to/from text format
    static String printToString(MessageOrBuilder message);
    static void merge(Readable input, Message.Builder builder) throws IOException;
    static Printer printer();
    static Parser parser();
}

class TextFormatParseException extends IOException {
    // Exception thrown when text format parsing fails
    String getMessage();
    int getLine();
    int getColumn();
}

class Extension<ContainingType, Type> {
    // Represents a protocol buffer extension
}

class ExtensionRegistry {
    // Registry for protocol buffer extensions
    static ExtensionRegistry newInstance();
    void add(Extension<?, ?> extension);
    ExtensionRegistry getUnmodifiable();
}

class ExtensionRegistryLite {
    // Lite version of extension registry
    static ExtensionRegistryLite newInstance();
}

class InvalidProtocolBufferException extends IOException {
    // Exception thrown when parsing invalid protocol buffer data
    static InvalidProtocolBufferException truncatedMessage();
    static InvalidProtocolBufferException negativeSize();
    static InvalidProtocolBufferException malformedVarint();
    static InvalidProtocolBufferException invalidTag();
    static InvalidProtocolBufferException invalidEndTag();
    static InvalidProtocolBufferException invalidWireType();
    static InvalidProtocolBufferException recursionLimitExceeded();
    static InvalidProtocolBufferException sizeLimitExceeded();
}

class UnknownFieldSet implements MessageLite {
    // Container for fields that were parsed but not recognized
    static UnknownFieldSet getDefaultInstance();
    static Builder newBuilder();
    Map<Integer, Field> asMap();
    boolean hasField(int number);
    Field getField(int number);
}