Possible addition to Mixin Examples External Link

static {
int i = 4;
}

public class ExampleMod implements ModInitializer {
    [...]
 
    @Override
    public void onInitialize() {
        AttackBlockCallback.EVENT.register((player, world, hand, pos, direction) -> {
            BlockState state = world.getBlockState(pos);
            /* Manual spectator check is necessary because AttackBlockCallbacks
               fire before the spectator check */
            if (state.isToolRequired() && !player.isSpectator() && 
                player.getMainHandStack().isEmpty()) {
                player.damage(player.getDamageSources().generic(), 1.0F);
            } 
            return ActionResult.PASS;
        });
    }
}