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Thread: Problem with array initialization

  1. #1
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    Default Problem with array initialization

    I have been working in creating a B+ tree. I have certain problem in code. Please tell me what are the errors and how can I overcome it? I am giving the snippet where the error occurs.

     
    class record
    		{
    			public int value;
    		}
     
     
    		class node
    		{
    			Object[] pointers ;
    			int[] keys;
    			node parent;
    			boolean is_leaf;
    			int num_keys;
    			node next;
    			record r;
    		}
     
                 node start_new_tree(int key, record pointer)
    	   {
     
    		System.out.println(key+pointer.value);
     
    		node root = d.makeleaf();
    		root.keys[0]=key;                                        // The error is here.It gives null pointer exception
    		root.pointers[0] = (Object)pointer;
    		root.pointers[order - 1] = null;
    		root.parent = null;
    		root.num_keys++;
     
    		//System.out.println(root.keys[0]+" "+root.pointers[0]+" "+root.num_keys);
    		return root;
    	}

    When I use start_new_tree in my main,this gives nullpointer exception at the place mentioned.Can you tell me how to overcome this?

    Thank you


  2. #2
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    Default Re: Problem with array initialization

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  3. #3
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    Default Re: Problem with array initialization

    Does method called makeleaf() initialize arrays of node class?
    For example:

    public node makeleaf(){
        node newnode = new node();
     
        ...
        newnode.num_keys = 5;
     
        // this line is important otherwise keys is null and throws NullPointerException
        newnode.keys = new int[newnode.num_keys];
        ...
     
        return newnode;
    }
    Last edited by gaszabo; April 4th, 2012 at 06:01 AM.

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