[Solved] NullPointerException at custom canInfuse() method

[Feronzed]

I have been trying to fix this crash for quite a while now.

 

Infusion Table tile entity class: [Link]

Minecraft crashes at canInfuse() method - line 261.

I am checking for null in both canInfuse method and RecipeInfusionTable class,

but the game still crashes.

Even if the return ItemStack is null, game shouldn't crash.

 

Help is much appreciated.

[larsgerrits]

Can you post the full crash log? Line 261 seems correct to me.

[TheGreyGhost]

Hi

 

Looks to me like RecipeInfusionTable.getRecipe is returning a null RecipeInfusionTable.  If you try to call .getOutput() on a null object, it will crash.

 

-TGG

 

[Feronzed]

No, I have changed the getOutput() code a bit to return netherrack ItemStack if it get's null, but it still crashes.

 

Here is a pastebin crash log (complete): [LINK]

Here is the line where crash occurs (I have edited the code a bit): [LINK]

 

[sequituri]

ItemStack itemStack = RecipeInfusionTable.getRecipe(this.infuserItemStacks[1], this.infuserItemStacks[2], this.infuserItemStacks[3]).getOutput();

Yep, it does indeed seem like the call to getOutput() is being made on a null recipe reference.

[line 40-RecipeInfusionTable.java] 		if (recipe == null) { return null; }

 

I think you should call your map's "containsKey(Arrays.asList ...)" function before assuming anything. My first problem is the way your recipeMap is implemented (as a HashMap with a key of "List<ItemStack>". That key is not likely ever to compare equally with another set of List<ItemStack> because the references are not the same. This is especially true when every ItemStack is freshly "new"ed each time. You might want to create a hash map ItemStackList with a HashCode and equals override. So as the check for equivalent ItemStacks in the list.

[Feronzed]

Ok, I'm writing this as I am debugging and writing the code.

I did what sequituri said, it didn't work, but instead of just returning null on !recipeMap.containsKey(Arrays.asList ... I added output on almost everything, so that I know where it crashes.

 

I figured it out! I was giving RecipeInfusionTable just a single null variable, it required four, 3 for input and 1 for output.

Now it doesn't crash, but it still isn't able to compare them.

And GUI seems to not update properly.

 

I have pushed latest version.

[TheGreyGhost]

Hi

 

I figured it out! I was giving RecipeInfusionTable just a single null variable, it required four, 3 for input and 1 for output.

Now it doesn't crash, but it still isn't able to compare them.

 

The reason it's not comparing properly is what sequitiri said in his last post.  If you compare objects in Java using ==, you are comparing whether they are the same object, not whether they have the same contents.  This is very important to keep in mind otherwise you'll have no end of strange bugs and headaches.

 

This link talks about it a bit more, for Strings.

 

http://stackoverflow.com/questions/513832/how-do-i-compare-strings-in-java

 

You could what Sequitiri suggested to fix this (i.e. create your "Three Input Items" class and give it an equals method), alternatively if you're just starting out you could compare the ItemStacks manually using ItemStack.areItemStacksEqual(itemstack1, itemstack2)

 

And come to think of it, you probably don't need your List, I think you could just use Map<ItemStack[], RecipeInfusionTable> instead

 

eg something like

 

private static Map<ItemStack[], RecipeInfusionTable>	recipeMap	= new HashMap();

for (Map.Entry<ItemStack [], RecipeInfusionTable> input : recipeMap.entrySet()) {
  if (     ItemStack.areItemStacksEqual(input.getKey()[0], firstInput) 
      && ItemStack.areItemStacksEqual(input.getKey()[1], secondInput)      
      && ItemStack.areItemStacksEqual(input.getKey()[2], thirdInput)  {
    found my recipe
    return result;
  }    
}

 

I haven't compiled it so the syntax might not be right but the idea should work - assuming you don't mind that the order of the matching has to be exactly the same (first item must match first recipe item, second item must match second item, etc).

 

-TGG

 

[Feronzed]

Thanks to everyone who helped, it works now, just need to fix GUI which I will do myself.