Odd NullPointerException

[vroominator]

Well Hi there. Recently, I've been getting a NullPointerException whenever I press a button in my gui and I'm not entirely sure why.

Here's what comes out in the console:

 

2012-08-24 18:42:49 [iNFO] [sTDERR] java.lang.NullPointerException
2012-08-24 18:42:49 [iNFO] [sTDERR] 	at net.minecraft.src.sorcery.TileEntityWandCrafting.craftWand(TileEntityWandCrafting.java:64)
2012-08-24 18:42:49 [iNFO] [sTDERR] 	at net.minecraft.src.sorcery.PacketHandler.onPacketData(PacketHandler.java:40)
2012-08-24 18:42:49 [iNFO] [sTDERR] 	at cpw.mods.fml.common.network.NetworkRegistry.handlePacket(NetworkRegistry.java:224)
2012-08-24 18:42:49 [iNFO] [sTDERR] 	at cpw.mods.fml.common.network.NetworkRegistry.handleCustomPacket(NetworkRegistry.java:212)
2012-08-24 18:42:49 [iNFO] [sTDERR] 	at cpw.mods.fml.common.network.FMLNetworkHandler.handlePacket250Packet(FMLNetworkHandler.java:63)
2012-08-24 18:42:49 [iNFO] [sTDERR] 	at net.minecraft.src.NetServerHandler.handleCustomPayload(NetServerHandler.java:1022)
2012-08-24 18:42:49 [iNFO] [sTDERR] 	at net.minecraft.src.Packet250CustomPayload.processPacket(Packet250CustomPayload.java:70)
2012-08-24 18:42:49 [iNFO] [sTDERR] 	at net.minecraft.src.MemoryConnection.processReadPackets(MemoryConnection.java:72)
2012-08-24 18:42:49 [iNFO] [sTDERR] 	at net.minecraft.src.NetServerHandler.networkTick(NetServerHandler.java:72)
2012-08-24 18:42:49 [iNFO] [sTDERR] 	at net.minecraft.src.NetworkListenThread.networkTick(NetworkListenThread.java:55)
2012-08-24 18:42:49 [iNFO] [sTDERR] 	at net.minecraft.src.IntegratedServerListenThread.networkTick(IntegratedServerListenThread.java:98)
2012-08-24 18:42:49 [iNFO] [sTDERR] 	at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:630)
2012-08-24 18:42:49 [iNFO] [sTDERR] 	at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:547)
2012-08-24 18:42:49 [iNFO] [sTDERR] 	at net.minecraft.src.IntegratedServer.tick(IntegratedServer.java:102)
2012-08-24 18:42:49 [iNFO] [sTDERR] 	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:453)
2012-08-24 18:42:49 [iNFO] [sTDERR] 	at net.minecraft.src.ThreadServerApplication.run(ThreadServerApplication.java:17)

 

 

My tile entity:

 

package net.minecraft.src.sorcery;

import net.minecraft.src.*;

import java.util.Random;

public class TileEntityWandCrafting extends TileEntity implements IInventory
{
    private ItemStack[] items = new ItemStack[4];

    public int getSizeInventory()
    {
        return 4;
    }
    
    public void craftWand()
    {
    	EnumWandMods[] wandMods = new EnumWandMods[3];
    	ItemStack wand = items[3];
    	ItemStack crystal = items[2];
    	ItemStack core1 = items[0];
    	ItemStack core2 = items[1];
    	
    	if(wand != null && crystal !=null)
    	{
    		if(wand.itemID == (new ItemStack(Sorcery.wand)).itemID && crystal.itemID == (new ItemStack(Sorcery.battery, 1, 0)).itemID && crystal.getItemDamage() == 0)
    		{
    			int j = 0;
    			
    			for(EnumWandMods mods : EnumWandMods.values())
    			{
    				if(core1 != null)
    				{
    					if(core1.itemID == EnumWandMods.values()[j].item.itemID)
    					{
    						wandMods[0] = SorceryHelper.getInstance().addWandMod(EnumWandMods.values()[j].item);
    						decrStackSize(0, 1);
   
    					}
    				}
    				
    				if(core2 != null)
    				{
    					if(core2.itemID == EnumWandMods.values()[j].item.itemID)
    					{
    						wandMods[1] = SorceryHelper.getInstance().addWandMod(EnumWandMods.values()[j].item);
    	        	    	decrStackSize(1, 1);
   
    					}
    				}
    				j = j+1;
    			}	
    			
    			decrStackSize(2, 1);
    			
    			wand.setTagCompound(new NBTTagCompound());
    			wand.stackTagCompound.setTag("mods", new NBTTagList("mods"));
    			NBTTagList list = (NBTTagList)wand.stackTagCompound.getTag("mods");
    			try
    			{
    				for(int i = 0; i < wandMods.length; i++)
    				{
    					NBTTagCompound tag = new NBTTagCompound();
    					tag.setInteger("ID", wandMods[i].modID); //<<--- Line 64
    					tag.setBoolean("Positive", wandMods[i].pos);
    					list.appendTag(tag);
    				}
    			}
    			catch(Exception e)
    			{
    				e.printStackTrace();
    			}
    		}
    	}
    }
    
    public ItemStack getStackInSlot(int par1)
    {
        return this.items[par1];
    }

    public ItemStack decrStackSize(int par1, int par2)
    {
        if (this.items[par1] != null)
        {
            ItemStack var3;

            if (this.items[par1].stackSize <= par2)
            {
                var3 = this.items[par1];
                this.items[par1] = null;
                this.onInventoryChanged();
                return var3;
            }
            else
            {
                var3 = this.items[par1].splitStack(par2);

                if (this.items[par1].stackSize == 0)
                {
                    this.items[par1] = null;
                }

                this.onInventoryChanged();
                return var3;
            }
        }
        else
        {
            return null;
        }
    }

    public ItemStack getStackInSlotOnClosing(int par1)
    {
        if (this.items[par1] != null)
        {
            ItemStack var2 = this.items[par1];
            this.items[par1] = null;
            return var2;
        }
        else
        {
            return null;
        }
    }

    public void setInventorySlotContents(int par1, ItemStack par2ItemStack)
    {
        this.items[par1] = par2ItemStack;

        if (par2ItemStack != null && par2ItemStack.stackSize > this.getInventoryStackLimit())
        {
            par2ItemStack.stackSize = this.getInventoryStackLimit();
        }

        this.onInventoryChanged();
    }

    public int func_70360_a(ItemStack par1ItemStack)
    {
        for (int var2 = 0; var2 < this.items.length; ++var2)
        {
            if (this.items[var2] == null || this.items[var2].itemID == 0)
            {
                this.items[var2] = par1ItemStack;
                return var2;
            }
        }

        return -1;
    }

    public String getInvName()
    {
        return "container.wandcrafting";
    }

    public void readFromNBT(NBTTagCompound par1NBTTagCompound)
    {
        super.readFromNBT(par1NBTTagCompound);
        NBTTagList var2 = par1NBTTagCompound.getTagList("Items");
        this.items = new ItemStack[this.getSizeInventory()];

        for (int var3 = 0; var3 < var2.tagCount(); ++var3)
        {
            NBTTagCompound var4 = (NBTTagCompound)var2.tagAt(var3);
            int var5 = var4.getByte("Slot") & 255;

            if (var5 >= 0 && var5 < this.items.length)
            {
                this.items[var5] = ItemStack.loadItemStackFromNBT(var4);
            }
        }
    }

    public void writeToNBT(NBTTagCompound par1NBTTagCompound)
    {
        super.writeToNBT(par1NBTTagCompound);
        NBTTagList var2 = new NBTTagList();

        for (int var3 = 0; var3 < this.items.length; ++var3)
        {
            if (this.items[var3] != null)
            {
                NBTTagCompound var4 = new NBTTagCompound();
                var4.setByte("Slot", (byte)var3);
                this.items[var3].writeToNBT(var4);
                var2.appendTag(var4);
            }
        }

        par1NBTTagCompound.setTag("Items", var2);
    }

    public int getInventoryStackLimit()
    {
        return 64;
    }

    public boolean isUseableByPlayer(EntityPlayer par1EntityPlayer)
    {
        return this.worldObj.getBlockTileEntity(this.xCoord, this.yCoord, this.zCoord) != this ? false : par1EntityPlayer.getDistanceSq((double)this.xCoord + 0.5D, (double)this.yCoord + 0.5D, (double)this.zCoord + 0.5D) <= 64.0D;
    }

    public void openChest() {}

    public void closeChest() {}
    
    @Override
    public void onInventoryChanged()
    {
    	
    }
}

 

 

This exception doesn't seem to hinder gameplay at all, but it's probably not a good idea for my mod to be pumping out exceptions all the time, so I want to fix it. Anyone know what's happening here? If you need more info, just ask.

[LexManos]

Seems fairly straight forward, you're trying to access something that is null.

For one thing, you're specifying wandMods is 3 elements, and on a good day you're only setting 2.

You need to lower the size of the array to a proper one, and also add in a null check before you try to access soemthing that is possibly null.

[vroominator]

Silly me.

Added in a null check and all is working fine.

Thanks lex.