So I'm programming a tile entity for an altar block which uses some code to store an item.

	    public void readFromNBT(NBTTagCompound compound)
	    {
	        super.readFromNBT(compound);
	        this.loadFromNbt(compound, true);
	    }

	    public NBTTagCompound writeToNBT(NBTTagCompound compound)
	    {
	    	NBTTagCompound itemTag = new NBTTagCompound();
	    	itemTag.setString("id", this.currentItem.getItem().getRegistryName().getResourceDomain() + ':' + this.currentItem.getItem().getRegistryName().getResourcePath());
	    	itemTag.setInteger("count", this.currentItem.getCount());
	    	itemTag.setInteger("data", this.currentItem.getItemDamage());
	    	compound.setTag("item", itemTag);
	    	compound.setBoolean("isValid", this.isValidAltar);
	    	super.writeToNBT(compound);
	    	return compound;
	    }
	    public void loadFromNbt(NBTTagCompound compound, boolean isLogging)
	    {
	        NBTTagCompound itemTag = (NBTTagCompound) compound.getTag("item");
	        String itemId = itemTag.getString("id");
	        Item item = GameRegistry.findRegistry(Item.class).getValue(new ResourceLocation(itemId));
	        int count = itemTag.getInteger("count");
	        int damage = itemTag.getInteger("data");
	        this.currentItem = new ItemStack(item, count, damage);
	        this.isValidAltar = compound.getBoolean("isValid");
	        if(isLogging)
	        {
	        	QuickLogger.log("itemTag = " + itemTag.toString() + "\nitemId = " + itemId + "\ncount = " + count + "\ndata = " + damage + "\nisAltarValid = " + compound.getBoolean("isValid"));
	        }
	    }

and I keep getting this error in the log even though everything stores and loads seemingly fine, it raises a java.lang.NullPointerException on the line in loadFromNbt() which gets the String itemId

Here's the little error traceback thing

[16:30:23] [main/FATAL] [minecraft/Minecraft]: Error executing task
java.util.concurrent.ExecutionException: java.lang.NullPointerException
	at java.util.concurrent.FutureTask.report(Unknown Source) ~[?:1.8.0_191]
	at java.util.concurrent.FutureTask.get(Unknown Source) ~[?:1.8.0_191]
	at net.minecraft.util.Util.runTask(Util.java:54) [Util.class:?]
	at net.minecraft.client.Minecraft.runGameLoop(Minecraft.java:1177) [Minecraft.class:?]
	at net.minecraft.client.Minecraft.run(Minecraft.java:441) [Minecraft.class:?]
	at net.minecraft.client.main.Main.main(Main.java:118) [Main.class:?]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_191]
	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_191]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_191]
	at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_191]
	at net.minecraft.launchwrapper.Launch.launch(Launch.java:135) [launchwrapper-1.12.jar:?]
	at net.minecraft.launchwrapper.Launch.main(Launch.java:28) [launchwrapper-1.12.jar:?]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_191]
	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_191]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_191]
	at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_191]
	at net.minecraftforge.gradle.GradleStartCommon.launch(GradleStartCommon.java:97) [start/:?]
	at GradleStart.main(GradleStart.java:25) [start/:?]
Caused by: java.lang.NullPointerException
	at thetrueskeptic.ebtks.tileentity.TileEntityAltar.loadFromNbt(TileEntityAltar.java:108) ~[TileEntityAltar.class:?]
	at thetrueskeptic.ebtks.tileentity.TileEntityAltar.readFromNBT(TileEntityAltar.java:91) ~[TileEntityAltar.class:?]
	at net.minecraft.tileentity.TileEntity.handleUpdateTag(TileEntity.java:361) ~[TileEntity.class:?]
	at net.minecraft.client.network.NetHandlerPlayClient.handleChunkData(NetHandlerPlayClient.java:836) ~[NetHandlerPlayClient.class:?]
	at net.minecraft.network.play.server.SPacketChunkData.processPacket(SPacketChunkData.java:110) ~[SPacketChunkData.class:?]
	at net.minecraft.network.play.server.SPacketChunkData.processPacket(SPacketChunkData.java:20) ~[SPacketChunkData.class:?]
	at net.minecraft.network.PacketThreadUtil$1.run(PacketThreadUtil.java:21) ~[PacketThreadUtil$1.class:?]
	at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) ~[?:1.8.0_191]
	at java.util.concurrent.FutureTask.run(Unknown Source) ~[?:1.8.0_191]
	at net.minecraft.util.Util.runTask(Util.java:53) ~[Util.class:?]
	... 15 more

 

Edited February 28, 20196 yr by TastesLikeBleach
Accidentally hit shift + enter like I was on discord which posted it before I was done.

Post your code as a GitHub repository. We can’t see line numbers on the forums

Could you please link a resource or something because I don't know how to do that.

Well, only thing I can say for sure is that something is null in TileEntityAltar line 108
 

Caused by: java.lang.NullPointerException
	at thetrueskeptic.ebtks.tileentity.TileEntityAltar.loadFromNbt(TileEntityAltar.java:108) ~[TileEntityAltar.class:?]

 

1. Indicate which line is line 108.

2. Add the @Override annotation to your methods.

3. Why are you calling loadFromNbt in your TileEntity#readFromNBT? The point of TileEntity#readFromNBT is to read the tile entity's data from the NBT. There is no need for creating another method.

Edited March 1, 20196 yr by DavidM

2 hours ago, DavidM said:

1. Indicate which line is line 108.

2. Add the @Override annotation to your methods.

	    public void loadFromNbt(NBTTagCompound compound, boolean isLogging)
	    {
	        NBTTagCompound itemTag = (NBTTagCompound) compound.getTag("item");
	      108 >>> String itemId = itemTag.getString("id");
	        Item item = GameRegistry.findRegistry(Item.class).getValue(new ResourceLocation(itemId));
	        int count = itemTag.getInteger("count");
	        int damage = itemTag.getInteger("data");
	        this.currentItem = new ItemStack(item, count, damage);
	        this.isValidAltar = compound.getBoolean("isValid");
	        if(isLogging)
	        {
	        	QuickLogger.log("itemTag = " + itemTag.toString() + "\nitemId = " + itemId + "\ncount = " + count + "\ndata = " + damage + "\nisAltarValid = " + compound.getBoolean("isValid"));
	        }
	    }

I should've overridden those methods, I'll do that now

1. Use ItemStack#serialize and ItemStack#deserialize to save your item in the altar. There is already built-in approaches to store inventory/itemstack to NBT. Don't reinvent the wheel.

2. itemTag is null, thus causing the error.

Edited March 1, 20196 yr by DavidM
Typo. Thanks Laike_Endaril.

Alright show's over, using @Override on the read and write methods fixed it.

55 minutes ago, DavidM said:

2. itemId is null, thus causing the error.

This is false

itemTag is the thing which is null, which means compound.getTag("item") returned null

1 hour ago, TastesLikeBleach said:

Alright show's over, using @Override on the read and write methods fixed it.

Adding @Override only tells your IDE that you intend to override a method. It does not have any affect of the flow of a program. 

5 hours ago, TastesLikeBleach said:

using @Override on the read and write methods fixed it.

1. @Override has absolutely no effect on the running of your code.

2. Again, do not build your own way of serializing an ItemStack. There is already a built-in method. In addition, your way of serializing did not include the NBT attached to the ItemStack.

 

4 hours ago, Laike_Endaril said:

itemTag is the thing which is null

Oops typo. I meant itemTag. Thanks for the correction.

Edited March 1, 20196 yr by DavidM