I want to bring some general functions of my mods in one separate mod (create something like API). How I can do this? Every mod in forge is singleton, so, can I call required API methods from API. instance? If I can, and how I will know if mod named API was already initialized? It must be initialized before any dependent mod use it. Is there a way to set mod load order?

Take a look at Mod annotation (I think it's what you want).

example:

@Mod(modid = "moen-jaffas-power", name = "Jaffas - power", version = Reference.Version, dependencies = "required-after:moen-jaffas;required-after:moen-monnef-core")
@NetworkMod(clientSideRequired = true, serverSideRequired = false)
public class mod_jaffas_power {
...

 

EDIT:

there is also soft dependency - without the "required" part, e.g.:

@Mod(modid = Reference.ModId, name = Reference.ModName, version = Reference.Version, dependencies = "after:Forestry;after:BuildCraft|Energy;after:ExtrabiomesXL")

TY. It will help me.

Replying for the sake of google. You can add dependencies "before" and "after", as well as specify required vesions:

"required-after:mod1@[1.0,)" - This means you require a mod with id "mod1" of version 1.0 and higher to be loaded before your mod.

See javadoc for cpw.mods.fml.common.versioning.VersionRange.createFromVersionSpec(String spec)