how to use an arraylist.

[roguehippo]

Hello forums, just a note before i start, i try to look up the answers for my questions on google before i come here to ask, and ive been trying for hours to get this to work to no avial. anyways, i have an arrayList of strings for a loot list (or atleast i think i do, every time i try to log the contents i just get a null pointer). anyways. im trying to turn the arraylist into an array so i can use it to find the closest ground item. 

here is my current function to determine if i should loot a stackable item. 

 

http://pastebin.com/rgxNpPbf

 

the arraylist is transfered from an arraylist from the gui using this.(which is called in onStart() )

 

 if(gui.UseLooting)

       {

    log("setting looting shit");

    UseLooting = true;

       

    LootListStackable = gui.StackableLootList;

       

    LootListNotStackable = gui.NonStackableLootList;

    log("DISPLAYING LISTS");

   // log(gui.StackableLootList.size());

    //log(LootListStackable.size()); commented out because they both caused null pointers

       }

 

the arraylists are declared in the gui like so

 

public ArrayList<String>  StackableLootList;

 

and contents are added to the list in the gui when a button is pushed like so

 

 StackableLootList.add(LootToAdd.getText());

 

i literally have no idea why i get a null pointer whenever i try to do anything with the array lists in my main code. please help

 

 

 

 

Edited May 21, 2016 by roguehippo

[Tom]

Post all of the relevant code so I can see your problem, and Ill answer everything in one reply.

Plz indent it properly as well, ty.

[Disposition]

Make sure that when you declare the list you instantiate it, i.e.

public ArrayList<String> StackableLootList = new ArrayList<>();

[FrostBug]

.NET conventions in Java ..

 

Anyway, we need to see whats going on in the gui class to identify the problem

[roguehippo]

Post all of the relevant code so I can see your problem, and Ill answer everything in one reply.

Plz indent it properly as well, ty.

 

here is the code for my gui. 

 

http://pastebin.com/HUNyAuFY

 

the adding of the strings when the loot button is pressed is at line 281.

 

here is my main code. 

 

http://pastebin.com/HsuELXZi

 

the looting functions are at the bottom

 

thanks

[Tom]

here is the code for my gui. 

 

http://pastebin.com/HUNyAuFY

 

the adding of the strings when the loot button is pressed is at line 281.

 

here is my main code. 

 

http://pastebin.com/HsuELXZi

 

the looting functions are at the bottom

 

thanks

 

public ArrayList<String>  StackableLootList;

public ArrayList<String>  NonStackableLootList;

 

Should be

 

public ArrayList<String>  StackableLootList = new ArrayList<>();
public ArrayList<String>  NonStackableLootList = new ArrayList<>();

[Woody]

String[] lootArray = new String[stackableLootList.size()];

 

StackableLootList.toArray(lootArray);

[roguehippo]

 

public ArrayList<String>  StackableLootList;

public ArrayList<String>  NonStackableLootList;

 

Should be

 

public ArrayList<String>  StackableLootList = new ArrayList<>();
public ArrayList<String>  NonStackableLootList = new ArrayList<>();

 

thanks so much for getting back to me i didnt know that initializing it in this specific way was necesarry or even made a difference. is it easy to explain why this makes a difference? (i just want to make my future coding as good as possible)

[Woody]

thanks so much for getting back to me i didnt know that initializing it in this specific way was necesarry or even made a difference. is it easy to explain why this makes a difference? (i just want to make my future coding as good as possible)

If you don't initialize a variable before you use it, it will return as null. There are some exceptions such as int, long etc.

[roguehippo]

i guess something else is wrong because im still getting null pointers when i do anything with the grounditem

[GaetanoH]

i guess something else is wrong because im still getting null pointers when i do anything with the grounditem

 

Just implement enough checks to see if the GroundItems are null? Just check out your logs there would be the exact line the program is throwing a NullPointer.

[Woody]

i guess something else is wrong because im still getting null pointers when i do anything with the grounditem

You have to define and do a null check before using it

[roguehippo]

Im posting here just so anyone else that has this problem can hopefully find the answer. After looking on many forums i found out the problem was actually due to an import mistake. i accidently imported like java.awt.List instead of java.util.List. -___-

[Acerd]

Im posting here just so anyone else that has this problem can hopefully find the answer. After looking on many forums i found out the problem was actually due to an import mistake. i accidently imported like java.awt.List instead of java.util.List. -___-

classic beginner mistake