Main.java:16: error: class ModItems is public, should be declared in a file named ModItems.java
public class ModItems {
       ^
Main.java:5: error: package mod.giac.item does not exist
import mod.giac.item.ItemGemstone;
                    ^
Main.java:6: error: package net.minecraft.client.renderer.block.model does not exist
import net.minecraft.client.renderer.block.model.ModelResourceLocation;
                                                ^
Main.java:7: error: package net.minecraft.init does not exist
import net.minecraft.init.Blocks;
                         ^
Main.java:8: error: package net.minecraft.item does not exist
import net.minecraft.item.Item;
                         ^
Main.java:9: error: package net.minecraft.util does not exist
import net.minecraft.util.ResourceLocation;
                         ^
Main.java:10: error: package net.minecraftforge.client.model does not exist
import net.minecraftforge.client.model.ModelLoader;
                                      ^
Main.java:11: error: package net.minecraftforge.event does not exist
import net.minecraftforge.event.RegistryEvent;
                               ^
Main.java:12: error: package net.minecraftforge.fml.common does not exist
import net.minecraftforge.fml.common.FMLCommonHandler;
                                    ^
Main.java:13: error: package net.minecraftforge.fml.relauncher does not exist
import net.minecraftforge.fml.relauncher.Side;
                                        ^
Main.java:14: error: package net.minecraftforge.oredict does not exist
import net.minecraftforge.oredict.OreDictionary;
                                 ^
Main.java:17: error: cannot find symbol
    public static final HashMap<ItemGemstone, ItemGemstone> GEM_TABLE = new HashMap<ItemGemstone, ItemGemstone>();
                                ^
  symbol:   class ItemGemstone
  location: class ModItems
Main.java:17: error: cannot find symbol
    public static final HashMap<ItemGemstone, ItemGemstone> GEM_TABLE = new HashMap<ItemGemstone, ItemGemstone>();
                                              ^
  symbol:   class ItemGemstone
  location: class ModItems
Main.java:19: error: package RegistryEvent does not exist
    public static void registerItems(RegistryEvent.Register<Item> event) {
                                                  ^
Main.java:19: error: cannot find symbol
    public static void registerItems(RegistryEvent.Register<Item> event) {
                                                            ^
  symbol:   class Item
  location: class ModItems
Main.java:22: error: cannot find symbol
    public static void registerGem(ItemGemstone normal, ItemGemstone broken, RegistryEvent.Register<Item> event) {
                                   ^
  symbol:   class ItemGemstone
  location: class ModItems
Main.java:22: error: cannot find symbol
    public static void registerGem(ItemGemstone normal, ItemGemstone broken, RegistryEvent.Register<Item> event) {
                                                        ^
  symbol:   class ItemGemstone
  location: class ModItems
Main.java:22: error: package RegistryEvent does not exist
    public static void registerGem(ItemGemstone normal, ItemGemstone broken, RegistryEvent.Register<Item> event) {
                                                                                          ^
Main.java:22: error: cannot find symbol
    public static void registerGem(ItemGemstone normal, ItemGemstone broken, RegistryEvent.Register<Item> event) {
                                                                                                    ^
  symbol:   class Item
  location: class ModItems
Main.java:28: error: cannot find symbol
    public static void registerItem(Item item, RegistryEvent.Register<Item> event) {
                                    ^
  symbol:   class Item
  location: class ModItems
Main.java:28: error: package RegistryEvent does not exist
    public static void registerItem(Item item, RegistryEvent.Register<Item> event) {
                                                            ^
Main.java:28: error: cannot find symbol
    public static void registerItem(Item item, RegistryEvent.Register<Item> event) {
                                                                      ^
  symbol:   class Item
  location: class ModItems
Main.java:32: error: cannot find symbol
    public static void registerItem(Item item, RegistryEvent.Register<Item> event, String oredictName) {
                                    ^
  symbol:   class Item
  location: class ModItems
Main.java:32: error: package RegistryEvent does not exist
    public static void registerItem(Item item, RegistryEvent.Register<Item> event, String oredictName) {
                                                            ^
Main.java:32: error: cannot find symbol
    public static void registerItem(Item item, RegistryEvent.Register<Item> event, String oredictName) {
                                                                      ^
  symbol:   class Item
  location: class ModItems
Main.java:17: error: cannot find symbol
    public static final HashMap<ItemGemstone, ItemGemstone> GEM_TABLE = new HashMap<ItemGemstone, ItemGemstone>();
                                                                                    ^
  symbol:   class ItemGemstone
  location: class ModItems
Main.java:17: error: cannot find symbol
    public static final HashMap<ItemGemstone, ItemGemstone> GEM_TABLE = new HashMap<ItemGemstone, ItemGemstone>();
                                                                                                  ^
  symbol:   class ItemGemstone
  location: class ModItems
Main.java:37: error: cannot find symbol
        item.setRegistryName(new ResourceLocation("giac:" + item.getUnlocalizedName().replaceFirst("item\\.|tile\\.", "")));
                                 ^
  symbol:   class ResourceLocation
  location: class ModItems
Main.java:41: error: cannot find symbol
            OreDictionary.registerOre(oredictName, item);
            ^
  symbol:   variable OreDictionary
  location: class ModItems
Main.java:44: error: cannot find symbol
        if (FMLCommonHandler.instance().getSide() == Side.CLIENT) {
            ^
  symbol:   variable FMLCommonHandler
  location: class ModItems
Main.java:44: error: cannot find symbol
        if (FMLCommonHandler.instance().getSide() == Side.CLIENT) {
                                                     ^
  symbol:   variable Side
  location: class ModItems
Main.java:45: error: cannot find symbol
            ModelLoader.setCustomModelResourceLocation(item, 0, new ModelResourceLocation(item.getRegistryName(), "inventory"));
                                                                    ^
  symbol:   class ModelResourceLocation
  location: class ModItems
Main.java:45: error: cannot find symbol
            ModelLoader.setCustomModelResourceLocation(item, 0, new ModelResourceLocation(item.getRegistryName(), "inventory"));
            ^
  symbol:   variable ModelLoader
  location: class ModItems
33 errors