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Thread: Issues with tree

  1. #1
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    Default Issues with tree

    Hi, I'm trying to build a simple heap Swing applet and the problem I have is I cannot output the contents of the nodes. In my paintComponents method, I read in an array from main method and store each element into a Node array (data member) in my Heap class which is a JPanel with the paintComponents method. The drawing of the binary heap tree is fine, but I wanted to make sure the data actually inserted, but when I go print it out, it prints out null for each of the array indices of the data member: Node (instance variable of the Heap class), but I checked and I did read in data from the array (from main) into each indice of this Node array. So my Heap class constructor has a parameter to read in an array from main method I mean. Any suggestions appreciated?

    I have another Node class that stores a left and right "pointers'" (references) to other Nodes and stores a data value which is from the this.array_of_int array data member in the Heap class below.

    so basically I have:
    Heap class extends JPanel
    {
       private Node nodes_array[];
       private int array_of_int[];
     
      //constructor that has parameter for the nodes_array which stores a Node object and another array that 
      //   reads in each integer from an array passed into constructor in main 
     
       public void paintComponents()
       {
           //draw a binary heap with n Nodes basd on this.array (data member passed to Heap class's constructor instance)
           //and each time this.node_array[i] = new Node(null, null, this.array[i] );
     
       }
     
      public void output_heap()
      {
              //for each item in node_arrays:
                    if current index is null//PROBLEM: why is it ALWAYS null if I am creating a new Node in the paintComponents //method above, this is where I am stuck and need some help...
                           output: null
                    else
                          output: element at this node_arrays index                      
               //end for-loop
       }
    }

    EDIT: Would it be that paintComponents should only deal with drawing and NOT anything else...I'll look into this too but any suggestions appreciated


  2. #2
    Super Moderator jps's Avatar
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    Default Re: Issues with tree

    //and each time this.node_array[i] = new Node(null, null, this.array[i] );
    I don't follow what you mean by that.
    Don't be shy to post the code you are working with.

    Suggestion to fix it yourself, verify the values passed to the constructor, verify the values when they are "read in from main method", verify the values at every point in the code until you find out why the values are not what was expected.

  3. #3
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    Default Re: Issues with tree

    That was a typo*** it should be:
    this.node_array[i] = new Node(xPosition, yPosition, this.array[i] )

    I have a separate Node class with constructor that has an int x and int y position because I would like to build my nodes to be separate objects to swap each node's value and the 3rd parameter of the Node constructor above which is the data value from the int array[] data member which is just a regular array with the values hardcoded (for now anyways).

    *So it's the problem I have with why in the output method above in the Heap class, it outputs null for each entry in the this.node_array if I am clearly inserting a new Node objet in the code snippet in this post and OP. Appreciate any help.

    At this stage, I just want to be able to output the nodes in the this.node_array array.

    import java.awt.*;
    import javax.swing.*;
     
    public class Heap extends JPanel
    {
      private int xPosition;//initialized in constructor
      private int yPosition;//same
      private int array[];//same
      private Node node_array[];//same
      private int nodes_to_draw;//same (in main a hard coded int array for now to use bottom-up build heap)
     
      //public Heap constructor
     
      public void paintComponent(Graphics g)
      {
              Graphics2d g2d = (Graphics2d)g;
               while ( nodes_to_draw > 0 )
                {
                      //if still nodes to draw at this level
                      g2d.setColor(Color.yellow);
    		 g2d.fillOval( first_node_startX, first_node_startY, this.width, this.height );
     
    	//add this position to cur Heap_Node obj (most important is the data and color to change during heap sort)
    	this.node_arr[i] = new Heap_Node( xPosition, yPosition, width , height, this.array[i] );
            System.out.println("Node " + i + ": " + this.node_arr[i].get_data());//I can output the data at each node, but then it's always null in the output
            //   each node's data in the output method below which is where I am stuck
     
                //if maximum number of nodes reached to draw at current level
                        //update total nodes to draw at next level
               }
      }
     
      public void output_heap_data()//Problem here, I am unsure why it outputs null if I am inserting into this.node_arr in the paintComponents method above
      {
    		for ( int i = 1; i < this.node_arr.length; ++i )
    		{
    			if ( this.node_arr[i] != null )
    				System.out.println("Data: " + this.node_arr[i].get_data());
    			else
    				System.out.println("Data: " + null);//PROBLEM I have is here: why is it null if I'm inserting into this.node_arr array in the paintComponents method above??
    		}
     }
    }
     
    }

    ALso, the reason I want to store the xPosition and yPosition in each Node object is to be able to find the graphic nodes drawn so that I can find the coordinates to change the value if I need to swap (for heap sort) by updating what the g.drawString method displays but if there is a simpler way I'd appreciate since I am just getting into Swing applets but I find it interesting

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