1 public class BinaryTreeNode 2 { 3     public Object data; 4      5     public BinaryTreeNode leftPointer; 6      7     public BinaryTreeNode rightPointer; 8      9     public BinaryTreeNode(Object data)10     {11         this.data = data;12     }13     14 }15 16 public class Solution17 {18     public void preOrder(BinaryTreeNode node)19     {20         if(node == null)21         {22             return;23         }24         25         visit(node);26         27         if(node.leftPointer != null)28         {29             preOrder(node.leftPointer);30         }31         if(node.rightPointer != null)32         {33             preOrder(node.rightPointer);34         }35     }36     37     public void visit(BinaryTreeNode node)38     {39         System.out.println(node.data);40     }41     42 }