Inserting strings in tree data structure in java

Hello I have got this  tree data structure implementation in java ,
however the problem I am facing is that somehow the add method does
seem to me that it is not working properly .
When I for example use  " public void CreateFromDefinition(String definition) "
and put in for example  " (A(B(E(K),F),C(G(L,M)),D(H,I(N),J))) " , then when I use
System.out.println(y.GetListDefinition());
then what I get for the output is  =

                         name : (A
                         Exception in thread "main" java.lang.NullPointerException
                     at ads2.ADS2Tree.CreateFromDefinition(ADS2Tree.java:72)
                     at ads2.Main.main(Main.java:90)
                         Java Result: 1

package ads2;

  /*
   * This class defines the top-level tree data structure.
  */


public class ADS2Tree
{
  // Default Constructor
  public ADS2Tree()
  {
  }
  
  // -------------
public ADS2TreeNode leftNode() 
{return root.left;}

public ADS2TreeNode rightNode() {return root.right;}

public static int getNodeValue() 
{
    return ADS2TreeNode.nodeValue;

}

  private ADS2TreeNode root;    
  
  
  // Takes a string input of a list structure that defines a tree
  // e.g. definition="(A(B(E(K),F),C(G(L,M)),D(H,I(N),J)))");
  // and sets up the internal tree structure to represent this structure
  // Any previous tree structure is overridden when this method is called
  public void CreateFromDefinition(String definition)
  {     
      int startofname = 0;
      ADS2TreeNode current = new ADS2TreeNode (definition) ; // "dummy"
      root = current ;
      
      //TreeNode current = null;
      for (int i = 0; i<definition.length(); i++)
      {   
          char val = definition .charAt(i);
          if ( val == '(' || val == ')' || val == ',')
          {
              if (startofname != i)
              {
                  String name = definition.substring(startofname,i);
                  System.out.println("name : " + name);
                  
                  ADS2TreeNode node = new ADS2TreeNode (name);
                  current.AddChild(node);
                  if (val == '(')
                  {
                    current = node ;
                  }
                  else if (val == ')')
                  {    
                        current = current.GetParent();
                  }
              
                  startofname = i + 1;
                  
              }
              
              root = root.GetChild(0);
              
              // current = current ;
          }
      }
      
  }
  
  // Returns a String containing the list format of the tree in the following format:
  // NodeName(Child1,Child2,...Childn)
  // For example: (A(B(E(K),F),C(G(L,M)),D(H,I(N),J)))
  public String GetListDefinition()
  {
          return "(" + root.toString() + " ) " ;
  //  return "Implement list output of this tree, for example: (A(B(E(K),F),C(G(L,M)),D(H,I(N),J)))";
  }

  // Returns a String contain the pre-order enumation of the tree data structure
  // The return type should just contain the name of the treenodes, separated by commas
  // For example: A,B,C,D,E,F,G

  
  public String GetPreOrder(ADS2TreeNode root) 
  {
      
      
  GetPreOrder(root.left);  
  GetPreOrder(root.right);  
  
		if (root == null)
			return "";

		String result = root.data;
		if (root.left != null)
			result += GetPreOrder(root.left);
		if (root.right != null)
			result += GetPreOrder(root.right);
		return result;

  
  }
  

  public String GetInOrder()
  {
    return null;
  }
  
  public String GetPostOrder()
  {    		      if (root == null)
			return "";

		String result = "";
		if (root.left != null)
			result += GetPreOrder(root.left);
		if (root.right != null)
			result += GetPreOrder(root.right);
		result += root.data;
		return result;
                          
  }

  
 private void GetBreadthFirstOrder(ADS2TreeNode root) 
  {
         GetBreadthFirstOrder(root);
  }
      

  public String GetBreadthFirstOrder() 
  {
      
     if (root == null)
          return root.GetData();
     
          System.out.print(root.data + " ");
      GetBreadthFirstOrder(root.left);
      GetBreadthFirstOrder(root.right);
    
    return null;
    
  }
  

  public int GetTreeDegree()
  {
    return GetTreeHeight(root);
  }
  

  public int GetTreeHeight()
  {  
     if (root==null)
     return 0;
    int x = GetTreeHeight(root.left);
    int y = GetTreeHeight(root.right);
    return (x>y?x:y)+1;
    
  }
  
  
     public int GetTreeNodeCount()
   {
      return GetTreeNodeCount(root);
   }
   private int GetTreeNodeCount(ADS2TreeNode p)
   {
      if(p == null) return 0;
      else
      if(p.left == null && p.right == null) return 1;
      else
      return GetTreeNodeCount(p.left) + GetTreeNodeCount(p.right);
   }

  public String toString()
  {
    return super.toString();
  }

    private int GetTreeHeight(ADS2TreeNode left) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }


  
}

package ads2;


public class ADS2TreeNode
{

  public String data;     // data about this node
  private ADS2TreeNode parent; // parent node
  public ADS2TreeNode child[];
  public int noOfChildren;
  private final int maxChildren = 10;
  // add in variables to hold one or more child nodes
  
  public ADS2TreeNode right; // right node
  public ADS2TreeNode left;
  public static int nodeValue;
  public ADS2TreeNode p;
  
   // Add required constructors
   public ADS2TreeNode()
   {
     child = new ADS2TreeNode[maxChildren];
     noOfChildren = 0;
   }

   public ADS2TreeNode(String definition) {  
       child = new ADS2TreeNode[maxChildren];
       noOfChildren = 0;
       data = definition;  
   }
  
  public String GetData()
  {
    return data;
  }
   
  public void SetData(String data)
  {
    this.data=data;
  }

  // returns the number of children this node has 
  public int GetNoOfChildren()
  {
      return noOfChildren;
  }
  
  public String toString()
  {
      
      String res = data;
      if ( noOfChildren != 0)
      {
     
      res += " ( " + child[0];
      for ( int i = 1; i < noOfChildren; i++)
          res+= "," + child[i];
      res+= ")";
           
       }
  
     return res; 
  }

    void AddChild(ADS2TreeNode node) 
    {
        // Checking whether there is enough space
        if(noOfChildren < maxChildren) {
            // Can add child
            node.parent = this;
            child[noOfChildren] = node;
            noOfChildren++;
        }
        // else { cannot add child } 
    }

    ADS2TreeNode GetParent() {
        return parent;
    }

    ADS2TreeNode GetChild(int i) {
         return child[i];
    }
    
    
}