查看 javap 输出，您会发现：

$ javap ProtocolPacket
public interface ProtocolPacket extends scala.Serializable{
    public abstract byte[] toByteArray();
}

和同伴对象：

$ javap ProtocolPacket$
public final class ProtocolPacket$ extends java.lang.Object implements scala.ScalaObject,scala.Serializable{
    public static final ProtocolPacket$ MODULE$;
    public static {};
    public void getStreamType(byte[]);
    public java.lang.Object readResolve();
}

这让我相信你可以写的Java：

this makes me believe in Java you can write:

ProtocolPacket$.MODULE$.getStreamType(/**/)