CODEWITHSUNDEEP
java
Brandon Cross
Brandon Cross

Reputation: 13

Index Out Of Bounds Exception

I am working on a minecraft mod. The id system for EntityC4 is not working. The code is

public static List C4 = new ArrayList();  

public static EntityC4 getitemfromnumber(int num)
{
    EntityC4 entity = (EntityC4)C4.get(num);

    return entity;
}
public static void createdetonater(EntityC4 c4, int num)
{
    C4.add(num, c4);


}
public static int getnum(){
     int num = 0;
      for(boolean a = true; a != false;){
          EntityC4 c = (EntityC4)C4.get(num);
          System.out.print("current num : " + num);

            if(c != null)
            {
                a = false;
            }else{
                System.out.print("entity " + num + " is null" );
         num++;
            }
      }
      return num;
   }

And when I use getnum() an error shows up that says

java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
    at java.util.ArrayList.RangeCheck(Unknown Source)
    at java.util.ArrayList.get(Unknown Source)

EDIT:Ty and the loop was supposed the first non-existent space in the list.

Upvotes: 1

Views: 6312

Answers (5)

Trevor Freeman
Trevor Freeman

Reputation: 7242

If you rewrite your loop to use a counter then it will avoid this error. I am not sure exactly what your code is trying to do though (return first non-null instance?), so the loop below may be incorrect.

If you are trying to store a map of ID to entity, then you should probably use a HashMap<Integer,EntityC4> instead.

for(int num = 0; num < C4.size(); num++)
{
    EntityC4 c = (EntityC4)C4.get(num);
    System.out.print("current num : " + num);

    if(c != null)
    {
        return num;
    } else
    {
        System.out.print("entity " + num + " is null" );
    }
}
// throw an exception or whatever else your code should do here...

Upvotes: 0

Kane
Kane

Reputation: 4167

Your error message tells you everything: you're trying to get the zeroth element from a list that has no elements. You probably need to add something to C4,

Upvotes: 0

mprabhat
mprabhat

Reputation: 20323

Your error is coming from

EntityC4 c = (EntityC4)C4.get(num);

which states your C4 is empty, you would like to do a not null and notEmpty check on your list.

In order to check the reason why C4 is empty do a trace on createdetonater and see where its being called.

Upvotes: 1

Gonzalo Garcia Lasurtegui
Gonzalo Garcia Lasurtegui

Reputation: 4941

C4 is obviously empty if you just call getNum(), thus the exception saying that the index you are accessing doesn't exist.

You might want to pre-populate the list by calling createdetonater(..)?

Upvotes: 1

Robin
Robin

Reputation: 36621

You create a new ArrayList C4, you never put anything in the List, and then you ask it for the element at index 0. This element does not exists since the List is still empty, and it throws an exception.

You can avoid this exception by adjusting your method

public static EntityC4 getitemfromnumber(int num)
{
  EntityC4 entity = null;
  if ( num >=0 && num < C4.size ){
    entity = (EntityC4)C4.get(num);
  }
  return entity;
}

This will avoid the exception, but you will get stuck in your loop since you never find the element (which isn't available in the list)

Upvotes: 5

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