参考以下程序：

import java.util.LinkedList;  
import java.util.Queue;  

public class DiffOddEven {  

    //Represent a node of binary tree  
    public static class Node{  
        int data;  
        Node left;  
        Node right;  

        public Node(int data){  
            //Assign data to the new node, set left and right children to null  
            this.data = data;  
            this.left = null;  
            this.right = null;  
            }  
        }  

    //Represent the root of binary tree  
    public Node root;  

    public DiffOddEven(){  
        root = null;  
    }  

    //difference() will calculate the difference between sum of odd and even levels of binary tree  
    public int difference() {  
          int oddLevel = 0, evenLevel = 0, diffOddEven = 0;  

          //Variable nodesInLevel keep tracks of number of nodes in each level  
          int nodesInLevel = 0;  

          //Variable currentLevel keep track of level in binary tree  
          int currentLevel = 0;  

          //Queue will be used to keep track of nodes of tree level-wise  
          Queue<Node> queue = new LinkedList<Node>();  

          //Check if root is null  
          if(root == null) {  
              System.out.println("Tree is empty");  
              return 0;  
          }  
          else {  
              //Add root node to queue as it represents the first level  
              queue.add(root);  
              currentLevel++;  

              while(queue.size() != 0) {  

                  //Variable nodesInLevel will hold the size of queue i.e. number of elements in queue  
                  nodesInLevel = queue.size();  

                  while(nodesInLevel > 0) {  
                      Node current = queue.remove();  

                    //Checks if currentLevel is even or not.  
                      if(currentLevel % 2 == 0)  
                          //If level is even, add nodes's to variable evenLevel  
                          evenLevel += current.data;  
                      else  
                          //If level is odd, add nodes's to variable oddLevel  
                          oddLevel += current.data;  

                      //Adds left child to queue  
                      if(current.left != null)  
                          queue.add(current.left);  
                      //Adds right child to queue  
                      if(current.right != null)   
                          queue.add(current.right);  
                     nodesInLevel--;  
                  }  
                  currentLevel++;  
              }  
              //Calculates difference between oddLevel and evenLevel  
              diffOddEven = Math.abs(oddLevel - evenLevel);  
          }  
          return diffOddEven;  
      }  

    public static void main (String[] args) {  

        DiffOddEven bt = new DiffOddEven();  
        //Add nodes to the binary tree  
        bt.root = new Node(1);  
        bt.root.left = new Node(2);  
        bt.root.right = new Node(3);  
        bt.root.left.left = new Node(4);  
        bt.root.right.left = new Node(5);  
        bt.root.right.right = new Node(6);  

        //Display the difference between sum of odd level and even level nodes  
        System.out.println("Difference between sum of odd level and even level nodes: " + bt.difference());  
}  
}

运行结果：

Difference between sum of odd level and even level nodes: 11