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Thread: Value is null even after i have allocated memory for the object

  1. #1
    Junior Member
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    Oct 2012
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    Default Value is null even after i have allocated memory for the object

    I am a total newbie in java , and i am facing this issue. after allocating memory for my class instance, i am not able to access the variable in this instance.
    here is the code for this.

    Main function:
      String ip=args[0];
                FileReader input = new FileReader(ip);
                BufferedReader bufRead = new BufferedReader(input);
                String line;
                int count = 0;
                line = bufRead.readLine();      // read first line
                int v = Integer.parseInt(line);
                //System.out.print("Value of number is "+ v);
    Graph createGraph(int v,Graph g1){
            g1.g=new Vertex[v];
        //    g1.g[0].id=4;
            System.out.println("value of g[0].id is"+g1.g[0].id );
            for (int i=0;i<v;i++)
                g1.g[i]=new Vertex();
            return g1;
    The output i am getting is :

    Exception in thread "main" java.lang.NullPointerException
    at graphcolouring.Graph.createGraph(Graph.java:21)
    at graphcolouring.GraphColouring.main(GraphColouring. java:29)
    Last edited by helloworld922; October 26th, 2012 at 10:09 AM. Reason: please use [code] tags

  2. #2
    Crazy Cat Lady KevinWorkman's Avatar
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    Default Re: Value is null even after i have allocated memory for the object

    What variable is null in that line?

    Also, declaring a variable does not initialize it. Until you initialize it, the variable's value is null.
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