将二叉树所有结点的左右子树交换并输出。

import java.util.*;      

public class BinaryTree {      
    protected Node root;      

    public BinaryTree(Node root) {      
        this.root = root;      
    }      

    public Node getRoot() {      
        return root;      
    }      

    /** 构造树 */     
    public static Node init() {      
        Node a = new Node('A');      
        Node b = new Node('B', null, a);      
        Node c = new Node('C');      
        Node d = new Node('D', b, c);      
        Node e = new Node('E');      
        Node f = new Node('F', e, null);      
        Node g = new Node('G', null, f);      
        Node h = new Node('H', d, g);      
        return h;// root      
    }      

    /** 访问节点 */     
    public static void visit(Node p) {      
        System.out.print(p.getKey() + " ");      
    }      

    /** 递归实现前序遍历 */     
     static void preorder(Node p) {      
        if (p != null) {      
            visit(p);      
            preorder(p.getLeft());      
            preorder(p.getRight());      
        }      
    }      



   /** 层次遍历*/  
   static void levelorder(Node p){      
        if(p==null) return;      
        Queue<Node> queue=new LinkedList<Node>();      
        queue.offer(p);      
        while(queue.size()>0){      
            Node temp=queue.poll();      
            visit(temp);    
            if(temp.getLeft()!=null){      
                queue.offer(temp.getLeft());      
            }      
            if(temp.getRight()!=null){      
                queue.offer(temp.getRight());      
            }      
        }      

    }      

   //将二叉树所有结点的左右子树交换   

static void swapTree(Node root){   

  if(root != null) {   

   Node tmp = root.getLeft();   
   root.setLeft(root.getRight());   
   root.setRight(tmp);   

   swapTree(root.getLeft());   
   swapTree(root.getRight());   

  }   
}   


  //输出二叉树的嵌套括号表示

   static void display(Node tree){
      if(tree!=null){
        System.out.printf("%c",tree.getKey());
        if(tree.getLeft()!=null||tree.getRight()!=null){
            System.out.printf("(");
            display(tree.getLeft());
            if(tree.getRight()!=null)
               System.out.printf(",");
            display(tree.getRight());
            System.out.printf(")");
         }
      }
    }


    /**    
     * @param args    
     */     
    public static void main(String[] args) {      
        BinaryTree tree = new BinaryTree(init());     

        display(tree.getRoot());
        System.out.printf("\n\n");
        swapTree(tree.getRoot());
        display(tree.getRoot());


    }       

} 

  public class Node {      
    private char key;      
    private Node left, right;      

    public Node(char key) {      
        this(key, null, null);      
    }      

    public Node(char key, Node left, Node right) {      
        this.key = key;      
        this.left = left;      
        this.right = right;      
    }      

    public char getKey() {      
        return key;      
    }      

    public void setKey(char key) {      
        this.key = key;      
    }      

    public Node getLeft() {      
        return left;      
    }      

    public void setLeft(Node left) {      
        this.left = left;      
    }      

    public Node getRight() {      
        return right;      
    }      

    public void setRight(Node right) {      
        this.right = right;      
    }      
}   

运行结果：
H(D(B(,A),C),G(,F(E)))

H(G(F(,E)),D(C,B(A)))
下载源码：