Hi, my problem is that I have an EntityThrowable and I must spawn it server-side, but then I need to do stuff when the entity hit something: on single player (internal server) all works perfect, but when I try to spawn that entity on a dedicated server some methods and classes don't exist and I run into an exception like NoClassDefFound. I post here a simple example, when I try it on a dedicated server and the entity hit somethings the server crash and I get a method not found error on the method e.setVelocity():

import net.minecraft.entity.EntityLiving;
import net.minecraft.entity.EntityLivingBase;
import net.minecraft.entity.player.EntityPlayer;
import net.minecraft.util.MovingObjectPosition;
import net.minecraft.world.World;

public class TestProj extends EntityThrowable {

private EntityPlayer caster;

public TestProj(World world, EntityLivingBase entity) {
	super(world, entity);
	this.caster = ((EntityPlayer)entity);
}

@Override
protected void onImpact(MovingObjectPosition mop) {
	if(mop.entityHit != null && mop.entityHit instanceof EntityLiving) {
		EntityLiving e = (EntityLiving) mop.entityHit;
		double vecX = caster.posX - e.posX, vecY = caster.posY - e.posY, vecZ = caster.posZ - e.posZ;
		e.setVelocity(vecX / 2.5, vecY / 3.5, vecZ / 2.5);
	}
	this.setDead();
}

}

How can I know which methods I can use on both sides? Or there is an other way to solve my problem?

If a method/class/field is not available on a specific side it will be marked with @SideOnly. So a method with @SideOnly(Side.CLIENT) can only be used on the client.

Thanks! Solved it! I just have to use e.addVelocity(), which isn't marked whit a @SideOnly annotation!