I'm trying to get the senses of a mob to modify them and EntityLiving.class.getDeclaredField("senses") works untill I'm in the dev enviroment, but as mod, i get java.lang.NoSuchFieldException.
I know I should change the "senses" string into the field_xxxxxx name, but how I can know the field's name?

Also, it may be better to use the ReflectionHelper class; that allows you to specify multiple field names (i.e. the deobfuscated one, the SRG name, and the Notch name) and the first one found will be used. Which means you can test the same code you build with and they'll both work

To explain more fully, reflection requires knowing the field / method names but Minecraft modding is working with "deobfuscated" version of the code which means the names we see in the mod environment are not the same as used in the actual Minecraft code. So you need to use a mapping -- in this case MCP which is why diesieben07 pointed you to it -- to use reflection on the right name. However, if you use the Minecraft name then it would not work in the development environment. So what you need to do is use the ReflectionHelper class so that both names are supported.

 

Basically, when using reflection in modding, don't use the standard Java reflection classes but use the ReflectionHelper class. Then make sure you put both versions of the name in as parameters to the ReflectionHelper methods.