I was trying to create an item which when used summons lightning on all entities of given type (currently trying on cods).

It should do essentially the same thing, as if you used the command :

/execute at @e[type=cod] run summon lightning_bolt

My try on this problem was the following piece of code:

@Override
public InteractionResult useOn(UseOnContext pContext) {
    ServerLevel world = ((ServerLevel) pContext.getLevel());

    for(LivingEntity entity: pContext.getLevel().getEntities()) {        //problem with this line

        if(entity.getType() == EntityType.COD){
            EntityType.LIGHTNING_BOLT.spawn(world, entity.blockPosition(), MobSpawnType.EVENT);
        }
    }

    return InteractionResult.SUCCESS;
}

 

but I was stopped by the following error before running the game:

'getEntities()' has protected access in 'net.minecraft.world.level.Level'

 

So what should I do? Is there some other way to iterate over all entities?

_level.getServer().getCommands().performPrefixedCommand(new CommandSourceStack(CommandSource.NULL, new Vec3(x, y, z), Vec2.ZERO, _level, 4, "", Component.literal(""), _level.getServer(), null).withSuppressedOutput(), "execute at @e[type=cod] run summon lightning_bolt");

should do it, I don't think it'll send a chat message every time. Code thing wasn't working so I had to do plain text.

_level.getServer().getCommands().performPrefixedCommand(new CommandSourceStack(CommandSource.NULL, new Vec3(x, y, z), Vec2.ZERO, _level, 4, "", Component.literal(""), _level.getServer(), null).withSuppressedOutput(), "execute at @e[type=cod] run summon lightning_bolt");

should do it, I don't think it'll send a chat message every time. Code thing wasn't working so I had to do plain text.

So I tried implementing what you sent like this:

@Override
public InteractionResult useOn(UseOnContext pContext) {
    ServerLevel world = ((ServerLevel) pContext.getLevel());

    world.getServer().getCommands().performPrefixedCommand(new CommandSourceStack(
      CommandSource.NULL, Vec3.ZERO, Vec2.ZERO, world, 4, "", Component.literal(""), world.getServer(), null).withSuppressedOutput(), "execute at @e[type=cod] run summon lightning_bolt");

    return InteractionResult.SUCCESS;
}

but now when I used the item, the game crashed with the following error:
 

class net.minecraft.client.multiplayer.ClientLevel cannot be cast to class net.minecraft.server.level.ServerLevel 
(net.minecraft.client.multiplayer.ClientLevel and net.minecraft.server.level.ServerLevel are in module [email protected] of loader 'TRANSFORMER' @5377414a)

I seems to me that "world.getServer()" returns ClientLevel instead of ServerLevel, but since I'm new to modding and Java, I don't know how to fix it.

(I thought, that if I declared "world" to be "ServerLevel", than "world.getServer()" would return ServerLevel not ClientLevel, so I'm lost)