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PONull Pointer Exception on first element add to my Generic ChunkList
 

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  1. PONull Pointer Exception on first element add to my Generic ChunkList
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    <p>So I have a null pointer exception when run. I am supposed to create a generic class that implements a list with chunks of arrays added as needed. Each time I add an element it is to check if there is space in the tail chunk array and if so add the element. Else it needs to add a chunk, adjust the pointers and add the element. My problem so far is that when I go to add the first element it is throwing a null pointer exception. I believe I have instantiated and object and assigned it where needed. If anyone has any insight please feel free to let me know what I am doing wrong or maybe its right in front of my face. </p> <p>"myChunk.chunk_.add(element);////////////error" is where I am getting the error. </p> <pre><code>package ChunkList; import java.util.*; import java.io.*; public class chunkList&lt;T&gt; { public static void main(String[] args) { chunkList&lt;Integer&gt; myList=new chunkList&lt;Integer&gt;(); for(int i=1; i&lt;24; i++) { myList.add(i);////////////////////////////////// System.out.println("Adding number: "+ i); } System.out.println(""); myList.display(); } private chunk head;//changed T to chunk private chunk tail;//changed T to chunk private int array_size=8; private int list_size; public chunkList()//Default Constructor { head=null; tail=null; list_size=0; } //public chunkList(chunkList copy){}// a copy constructor.... don't think I need. class chunk// added &lt;T&gt; { //T[] chunk_arr = new T[array_size];// illegal operation //ArrayList&lt;T&gt; chunk_ = new ArrayList&lt;T&gt;(array_size); ArrayList&lt;T&gt; chunk_; private int chunk_size; //may need to change to public chunk nextChunk;//changed T to chunk chunk prevChunk;//changed T to chunk public chunk()//default constructor { chunk_ = new ArrayList&lt;T&gt;(array_size); chunk_size=0; nextChunk=null; prevChunk=null; } } public void add(T element) { if(this.tail==null)//empty chunk list { chunk myChunk=new chunk();//instantiate //myChunk.prevChunk=null;//changed from head to null //myChunk.nextChunk=null;//changed from tail to null head=myChunk; tail=myChunk; //head.nextChunk=null; //head.prevChunk=null; myChunk.chunk_.add(element);////////////error list_size++; myChunk.chunk_size=1; } else if (this.tail.chunk_size&lt;array_size)//adds the element to the last chunk in list { this.tail.chunk_.add(element);//add element list_size++; this.tail.chunk_size++;//increase individual chunk array size } else// create new chunk, relink chunks, add element { chunk myChunk=new chunk(); myChunk.chunk_size=1; list_size++; myChunk.chunk_.add(element); tail.nextChunk=myChunk; myChunk.prevChunk=tail; tail=myChunk; }} public int size() {return list_size;} public void display() { chunk my_chunk=head; if(my_chunk==null) { System.out.print("Empty Chunk List"); return; } for(int i=0;i&lt;list_size; ) { for(int j=0; j&lt;my_chunk.chunk_size; j++) { System.out.println(my_chunk.chunk_.get(j)); i++; } if(my_chunk.nextChunk!=null) my_chunk=my_chunk.nextChunk; } } } </code></pre> <p>So thanks Olivier Jacot-Descombes , I fixed one problem with the code and it now adds the first chunk BUT it is throwing NPE when it tries to create the next chunk. I will look at it and be back if i need more help. Thanks All.</p> <p>P.S. The add method on this was incorrectly linked together in the last else statement.</p>
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    1. This table or related slice is empty.
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    1. USaaron burns
    1. USaaron burns
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    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
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      1. PONull Pointer Exception on first element add to my Generic ChunkList
      1. This table or related slice is empty.
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    1. COAnother effective technique is to explain your code to someone else. This will often cause you to explain the bug to yourself. Sometimes it takes no more than a few sentences, followed by an embarrassed "Never mind, I see what's wrong. Sorry to bother you." This works remarkably well; you can even use non-programmers as listeners. One university computer center kept a teddy bear near the help desk. Students with mysterious bugs were required to explain them to the bear before they could speak to a human counselor. ~Brian Kernighan and Rob Pike, about debugging
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      1. USMartín Canaval
    2. CO1. You code is really messy. Please review http://www.oracle.com/technetwork/java/codeconventions-150003.pdf. 2. The NPE is thrown because you do not instantiate the `ArrayList<T> chunk_`. PLace a breakpoint at theis line `myChunk.chunk_.add(element)` and review carefully what is going on in side your default c'tor of the chunk<T> class.
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      1. USaviad
    3. COWhen ever I call "chunk myChunk=new chunk();//instantiate" does that not then call the default constructor for the chunk class and within that constructor it instantiates the "ArrayList<T>(array_size)"?
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      1. PONull Pointer Exception on first element add to my Generic ChunkList
      1. USaaron burns
 

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