Alright, so for context, I'm a new modder and I've come back to learning java after a while. I forgot most of my java knowledge from a while back, so I re-learned it, and I felt confident enough to try minecraft modding, but I have a problem with custom block entities.

I am trying to create a custom block entity called "Altar of Essence", but I have a problem with the code, and I do not know where to even start fixing it. 

My BlockEntity class:

public class AltarOfEssenceBlockEntity extends BlockEntity implements MenuProvider {
    private final ItemStackHandler itemHandler = new ItemStackHandler(3) {
        @Override
        protected void onContentsChanged(int slot) {
            setChanged();
        }
    };

    private LazyOptional<IItemHandler> lazyItemHandler = LazyOptional.empty();

    public AltarOfEssenceBlockEntity(BlockPos pos, BlockState state) {
        super(p_155228_, pos, state);
    }

    @Override
    public Component getDisplayName() {
        return Component.literal("Altar of Essence");
    }

    @Nullable
    @Override
    public AbstractContainerMenu createMenu(int id, Inventory inventory, Player player) {
        return
    }

    @Override
    public @NotNull <T> LazyOptional<T> getCapability(@NotNull Capability<T> cap, @Nullable Direction side) {
        if(cap == ForgeCapabilities.ITEM_HANDLER) {
            return lazyItemHandler.cast();
        }

        return super.getCapability(cap, side);
    }

    @Override
    public void onLoad() {
        super.onLoad();
        lazyItemHandler = LazyOptional.of(() -> itemHandler);
    }

    @Override
    public void invalidateCaps() {
        super.invalidateCaps();
        lazyItemHandler.invalidate();
    }

    @Override
    protected void saveAdditional(CompoundTag nbt) {
        nbt.put("inventory", itemHandler.serializeNBT());

        super.saveAdditional(nbt);
    }

    @Override
    public void load(CompoundTag nbt) {
        super.load(nbt);
        itemHandler.deserializeNBT(nbt.getCompound("inventory"));
    }

    public void drops() {
        SimpleContainer inventory = new SimpleContainer(itemHandler.getSlots());
        for (int i = 0; i < itemHandler.getSlots(); i++) {
            inventory.setItem(i, itemHandler.getStackInSlot(i));
        }

        Containers.dropContents(this.level, this.worldPosition, inventory);
    }
}

And my Block class:

package net.natan.natansrealmmod.block.custom;

import net.minecraft.core.BlockPos;
import net.minecraft.server.level.ServerPlayer;
import net.minecraft.world.InteractionHand;
import net.minecraft.world.InteractionResult;
import net.minecraft.world.entity.player.Player;
import net.minecraft.world.level.Level;
import net.minecraft.world.level.block.BaseEntityBlock;
import net.minecraft.world.level.block.RenderShape;
import net.minecraft.world.level.block.entity.BlockEntity;
import net.minecraft.world.level.block.entity.BlockEntityTicker;
import net.minecraft.world.level.block.entity.BlockEntityType;
import net.minecraft.world.level.block.state.BlockState;
import net.minecraft.world.phys.BlockHitResult;
import net.minecraftforge.network.NetworkHooks;
import org.jetbrains.annotations.Nullable;

public class AltarOfEssenceBlock extends BaseEntityBlock {

    public AltarOfEssenceBlock(Properties properties) {
        super(properties);
    }

    /* BLOCK ENTITY */

    @Override
    public RenderShape getRenderShape(BlockState p_49232_) {
        return RenderShape.MODEL;
    }

    @Override
    public void onRemove(BlockState pState, Level pLevel, BlockPos pPos, BlockState pNewState, boolean pIsMoving) {
        if (pState.getBlock() != pNewState.getBlock()) {
            BlockEntity blockEntity = pLevel.getBlockEntity(pPos);
            if (blockEntity instanceof AltarOfEssenceBlockEntity) {
                ((AltarOfEssenceBlockEntity) blockEntity).drops();
            }
        }
        super.onRemove(pState, pLevel, pPos, pNewState, pIsMoving);
    }

    @Override
    public InteractionResult use(BlockState pState, Level pLevel, BlockPos pPos,
                                 Player pPlayer, InteractionHand pHand, BlockHitResult pHit) {
        if (!pLevel.isClientSide()) {
            BlockEntity entity = pLevel.getBlockEntity(pPos);
            if(entity instanceof AltarOfEssenceBlockEntity) {
                NetworkHooks.openScreen(((ServerPlayer)pPlayer), (AltarOfEssenceBlockEntity)entity, pPos);
            } else {
                throw new IllegalStateException("Our Container provider is missing!");
            }
        }

        return InteractionResult.sidedSuccess(pLevel.isClientSide());
    }

    @Nullable
    @Override
    public BlockEntity newBlockEntity(BlockPos pos, BlockState state) {
        return new AltarOfEssenceBlockEntity(pos, state);
    }

    @Nullable
    @Override
    public <T extends BlockEntity> BlockEntityTicker<T> getTicker(Level level, BlockState state, BlockEntityType<T> type) {
        return super.getTicker(level, state, type);

        return createTickerHelper(type, );
    }
}

The problem I am facing here is that in the Block class, under the OnRemove override, use override and newBlockEntity override, AltarOfEssenceBlockEntity turns red and the error message I get is "cannot resolve symbol". What does this mean, and how can I fix it???

Never mind; it was a simple fix. I invalidated my caches then imported the class.