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First Java Assignment, simple problem with code.

 
Greenhorn
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Hi,

I'm doing my first java assignment and I'm almost finished, but I keep getting an error in the same place, so I took the part of the code out of the assignment project and tried to run it by itself, but I still can't figure out what's wrong. Here is the code:

I get the error:

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 2, Size: 1
at java.util.ArrayList.RangeCheck(Unknown Source)
at java.util.ArrayList.get(Unknown Source)
at nodeArray.getElement(nodeArray.java:12)
at Test.main(Test.java:19)





Any help would be appreciated, thanks!
 
Ranch Hand
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9
Scala Java
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this line:
i = 2*i + 2;
evaluates to 2 which is beyond the size 1(apparently)
also this line makes no sense:
nodeArray.getElement(i);
you are retrieving the element but doing nothing with it
the real problem seems to be here:
if(nodeArray.getElement(i) == null)
if(nodeArray.getElement(2) == null) when there is no element 2

this line also does nothing:
public int i = 0;
in the whole rest of that class all the i's are local variables passed to the methods.

 
J Doyle
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Randall Twede wrote:this line:
i = 2*i + 2;
evaluates to 2 which is beyond the size 1(apparently)
also this line makes no sense:
nodeArray.getElement(i);
you are retrieving the element but doing nothing with it
the real problem seems to be here:
if(nodeArray.getElement(i) == null)
if(nodeArray.getElement(2) == null) when there is no element 2



Thanks for the reply, I realised this a few minutes ago, so I made a new method in the nodeArray class:



And tested the following code:



And it still says that the size of nodeArray is 1.. What am I doing wrong?
 
Randall Twede
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not sure, sorry. someone else can help i am sure. i do know that now this line
nodeArray.increaseSize(2*i + 2);
equals 6 which is probably not what you intended.

 
J Doyle
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Randall Twede wrote:not sure, sorry. someone else can help i am sure. i do know that now this line
nodeArray.increaseSize(2*i + 2);
equals 6 which is probably not what you intended.



Yeah, I just wanted to see if its size increased, it didn't really matter what number I chose. Thanks anyway, I hope someone else knows...
 
Randall Twede
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public ArrayList<String> Array = new ArrayList<String>();

your variable should be all lowercase "array" not "Array"
only class and interface names start with a capital letter
this may have been the whole problem to begin with
 
Randall Twede
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change the name of the ArrayList to "array", or even better maybe "theArray"
i would also change public int i = 0; to public int index = 0; //will clarify things
i think you meant do
this.i = i;
in some of your methods

i like
index = i;
better
 
Rancher
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J Doyle wrote:Thanks for the reply, I realised this a few minutes ago, so I made a new method in the nodeArray class:


You need to understand the difference between the size and the capacity of an Arraylist.
The size is the number of elements it currently contains - you can only add a new value to an Arraylist when index >= 0 and index <= size.
The capacity is the size of the array that the ArrayList uses in the background to store values, but it only uses contiguous elements of the array i.e. a value cannot be added to element 4 of the array until values have been added to elements 0 - 3.
 
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Is this error still occuring? If so, I would like to see the complete code again after the changes in order to see if I can hunt down the issue. By the way, did you look up what an IndexOutOfBoundsException is, and how an ArrayList works with the proper java library methods?
 
Randall Twede
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i am guessing that J figured it out by now. if not feel free to keep asking. that is why we are here after all.
 
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